Can a boat's wake "flip" a tube? I have never been remotely close to "flipping" in thirty years of tubing and fishing from a boat wake or any other reason. I often take splash whereby my fishing jacket keeps me dry. When you see a boat making a big bow wake, you simply turn your craft to either take it from the side or the back.   Tubes ride over waves. Maybe a 10' surf at the seaside could do it but I've not seen a lake wave capable yet and I'm fishing a long time in winds to force 6 all everywhere, force 5 on large lakes.

Water skiers and personal water craft are not good. It's a bad idea to tube in close proximity to power boats. After dark, other boaters  can represent a collision risk if a tuber fails to display lights. Read the Salt Water Tubing section for advice about navigation lights, air horn sirens and visibility flags. Use your lights after dark whenever engines are running on the lake.

A 14-15' lake boat on Lough Ennell, Ireland in a 12kph wind (beaufort force 2-3).
This photo taken from my float tube. Ideal fishing conditions for both types of fishing craft. The boat covers more water, in a quick once over fashion. The tube covers less water more effectively due to less disturbance.
Both are practical solutions to fly fishing afloat.

Most people sit in the middle of a small boat seat, but a few "landlubbers" will sit away over on the side of the seat of a small boat, causing the boat to "list" or heel over. Then I must move my weight and sit on the opposite side of my seat to balance things up. These guys are still able to float tube safely. But for them to be safe they need to get a much bigger size tube than I do. Preferably with a lower seat too. That's all. These guys need a lower seat than me because they just need extra stability, like a newbie kayaker. But we can all tube just fine, so long as we choose a small water craft that suits our physique, and our ability.

That's small boats, now lets look at the same issues in a float tube. All you do is sit straight, sit upright, and you're fine, and you will enjoy yourself in your tube. The tube by design is extremely steady and very tolerant of bad balance and leaning away from the centreline.

Consider the tube in a wave. We float like a cork, impossible to sink. We go up the face of a wave and down the sloping far side again. I have tubed in 4-5 foot waves with no danger at all. If a wave breaks against our side, the splash drains right out again, unlike a boat which fills up. We cannot be swamped, broaching waves will sink dinghies under about 14' if they attempt to travel up or across wind, but not tubes. Traditional lough boats 18' - 19' have high sides to keep the water out. We are like a decked boat with totally enclosed buoyancy. We self drain and have no concerns about bilge water, there is no such worry for a float tuber. High sides are not required when your craft self drains.

If I really wanted to demonstrate a capsize a float tube here's what I'd do: An open front v-tube has a little less floatation facing the open side, the gap between the sponsons. If while climbing the slope up to a wave crest you then get your body high and at the same time lean hard over towards the opening of the already tilted tube, I guess you could roll it.  At least that is the way I assume it could be done. I have never been desperate or dumb enough to try it. And, I have NEVER been in even the remotest danger of doing so. A small boat is a thousand times easier to flip. As described above, my personal experience is that a few novices flip dinghies under 14' with ease.

Hard hulled boats can crash against rocks and crack and break. Then a boat not stuck on the rock fills up and sinks. But a tube is a soft craft that bounces against hard objects like rocks. We can paddle up to a rock, sit on it, maybe stand to stretch our legs, and have a cast all around, then move to the next rock. Rocks don't break tubes, they break boats. Boats have to be wary about running up on rocks at speed under power. Rocks are no problem at all in a tube going at a walking speed.

The manufacturer's weight rating of a tube is an indication, however it's just part of the picture. The height of the angler also affects stability, and taller should be treated the same as heavier weight when choosing the most suitable tube to buy.
If you think that you happen to have an "iffy small boat balance sense" this should also suggest the choice of a tube rated for greater weight than your actual weight, or of greater diameter sponsons so safety is not reduced.

The safety strap buckle.  Say we do manage to invert our float tube. We must exit the tube without more than a few seconds delay, get into a heads up attitude, and then sort things out. That's why ALL ROUND TUBES WITH A CROTCH STRAP HAVE A QUICK RELEASE CLIP FITTED AS STANDARD. Vee tubes mostly have no crotch strap so to exit an open front vee tubes is simplicity: step forward, done.
I wonder how many small boat users of all sorts have mentally or actually rehearsed the sequence of actions that will accomplish this safely and quickly, or what items of tackle might block and tangle and have to be dealt with. So make your quick release from tube and tackle exit plan. It's necessary (even if never used) to have it pre-figured out, just like an office fire safety drill.

The tube is stable - but it handles waves better than wind. Going up and down is fun, but makes line control very difficult. That undoubtedly reduces the effectiveness of my fishing technique, particularly bite detection and successful striking. Sonar display is compromised and draws a sawtooth bottom on the screen, but otherwise still functions ok. For these reasons, there is a certain bad weather threshold above which that you cease to want to go out in, because the fishing will be harder.
In a bigger wave the fin kicking action is quite difficult. Often while kicking, the tube will pitch up where it was going down or vice versa and this leaves a fin deeper than planned, or popping out of the water surface making an unwanted splash and losing the power of that kick. I don't like that, and it does take from the fun.
Although a tube handles waves well, it does not go against a wind well, it's very tiring. Fin power is 1/2 horsepower, and a windy day is the very time when a boat with an outboard motor of several HP is more attractive!
What we are doing in our tube can be summed up as learning how to boat efficiently with a low power unit (our legs) by avoiding doing the things that demand high power, like high speed, going out long distance to the middle where wind and wind induced currents are stronger and increase the power requirements to move along.

Now for the "plus" the pros, magazines and books don't mention about wind on stillwater:
Equipment required: backpack straps for walking tube to the best shoreline, anchor and line.
The most important thing about tubing in a bigger wind and the "lee shore" waves is that we stay in close to the shore. We walk it or fin it in an upwind direction so we will be blown back home when we finish. We bring one or two anchors so we can go out 30 - 100 metres, no more, drop anchor and fish back into the lee shore we left from, where fish feed. There's not much need to go further in those conditions. The waves might break over the tube from behind but at anchor that's ok and provided  you're dressed for wet conditions, it's quite exhilarating fishing.

After blowing for an hour a fresh wind will setup a current on the surface layer of a lake flowing downwind at about 1/10th to 1/3 the windspeed. So kicking fins against a 15mph / bft force 4 / 22kph wind, then involves simultaneously kicking "upstream" what is effectively, a 5mph river at the same time. And a tube does 1 - 2mph max cruise speed, all higher speeds being "sprint" and unsustainable for an extended time, so accept that you won't beat that current for long, just a few minutes. If caught, go across and downwind to a landing place, as going upwind will cause you to "run-on-the-spot" with no benefit until you tire and "lose it" drifting downwind anyway.
What you can do, is power-fin your craft upwind a mere 30-50 metres from the downwind, lee shore and then stop and turn, drop anchor to rest your legs, casting back downwind towards the wave lashed shore you just came from. That's where the fish will be. They will be swimming along the shoreline so they come to you if you stay in one spot.

So the effort required is the downside. The upside is: all the fish food on the lake's surface layer is travelling by wind and current towards the downwind or lee shore, and the fish go there to feed, and they are close to the shore, where the downwind current/breeze takes them, located in the magic place just before the water current dives down and underneath it flows back upwind along the lake bottom. The taking place is a band of water a certain distance out from the dropoff parallel to the shoreline.

You will have it all to yourself and other tubes. This is a place boats fear to go because the waves can drop their breakable hardshell craft onto a rock causing expensive damage. They will stay further out if they come here at all, too far for their own good. The shore based anglers can't compete because they have a big wind in their face, and waves crashing in on top of their casting position. Life is uncomfortable and chaotic for them there. So all the competition goes elsewhere. The tube's superiority as a water craft really works to your advantage in this place at this time.

One important point: if you can't handle the breeze on an exposed windy wavy lee shore in your tube, don't try, and in so doing put yourself in danger. There is another way which we look at next.

You can alternatively go upwind to the windward shore which is sheltered and calm, at least it is near the shore, and as you move out it becomes a ripple, and then a wave as the wind picks up strength the farther you go away from shelter.
Anyway, the lake's sunken wind driven upwind current wells up in this zone. Bottom dwelling insect food items get lifted up to the surface here against their better judgment, and get eaten by fish that wait for them.
Also, quantities of terrestrial insects from trees and bushes will be blown onto the water and get eaten. There are two places to watch: the edge of the ripple which is where the terrestrials land, and the place at the shallows edge where the upwelling occurs and midge pupae and bloodworms are brought up. In a stratified lake this zone might be deoxygenated and easily dismissed. But trout have been proven to enter both warm and deoxygenated water for easy pickings, in conditions that are lethal to them if they stay there. But they are willing to do a snatch and grab and retreat to the cooled airy ripple, then come back.

In a diamond or square shape lake the upwelling can be funnelled into a narrow spot, and what a transient hotspot it is! Perfect for tubing, in the calm or slight ripple, and on a day when you have the lake to yourself. But be most careful not to be swept out, because you chose the upwind side.

I reckon on windy days surface feeder species go 50% downwind to the lee shore, 30% upwind to the upwelling zone and 20% to where terrestrials land beside the upwelling zone, and the rest of the lake is cleared out with the exception of minor "holding areas" around reefs, headlands and islands which exhibit mini versions of some of the wind driven attractions mentioned above. The bottom current moves bottom feeder species onto these places. Predators follow the active prey fish and many will show up in the windy zones to predate on the smaller fish feeding there.
In short, it's a time to fish, if you can.

But a warning for beginners: in those conditions everything must be organised, pre-figured out, and good equipment used, both tubing and clothing. You have to have tubing experience, and built up skills and adequate fitness.

Floatation fishing is inherently safer than most small to medium boat fishing ... you carry more backup systems onboard, and are harder to upset ... if you learn the basic skills, exercise proper precautions and wear your required devices. Tubes can handle big waves that other small boats cannot.  Tubes are flexible and bump off obstructions like rocks, on the other hand those rocks will crunch boats up and sink them.
For the average person, a big heavy 18' lake boat with an engine may be best on a rough windy day, but with clever watercraft know-how, intelligent location selection, good equipment, and a reasonably close launching point, a tube can still do the business.
Compared to a dinghy of 10-14' length the tube is better in waves and rough water due to the dinghy being unsafe and unable to go out for fear of swamping by waves coming over the side.
Compared to a dinghy in calm conditions the dinghy has the advantage, due to being able to cover more water, but is still more difficult to carry, tow, equip and purchase.
Compared to a 19' Burke lough boat? One that was designed for force 5-7 winds and huge waves. A Burke, Sheelin or Meagher dominates them utterly. It is an answer for rough conditions. BUT in calm weather it is a fish scaring monster that rattles when waves lap against it's hull and leaves a track of disturbed water behind it as it goes about the lake. The owners of lough boats have usually invested so much cash in their boat and engine and trailer that they are very proud of it and can never admit it's deficiencies as a FISHING CRAFT. They don't notice the 2-3 EMPTY SEATS their boat has anymore. But for fine weather fishing a heavy lough boat is clumsy in all but the hands of exceptionally gifted boatmen. It's engine, wave noise and dark shadow clears the shallows of taking fish. It's a good answer for the huge wild loughs like Corrib and Mask, cold early season fishing conditions, and windy days.
Maturity is accepting your limitations. These craft are limited, and so are tubes. All boats are a compromise. It's just which compromise suits the way and time and place we fish best? If you are truly honest about your mode of use, the correct water craft picks itself.

Final answer? The majority of anglers fish in moderate conditions, so where is the need for boats the size of the Queen Mary coming from? It comes from the competition fishing fraternity who must go out on a match date, whatever the weather, and have only one boat. These people want to race up the lough to get there before the other chaps with similar rigs. Competition fly fishers are in an "arms race" of their own making and are unaware of the fact. These people say: get a 19' Burke and a 25HP engine! Many of them need assistance to even get that big out board out of the car!
That's a cumbersome expensive choice for the angler who fishes the lake on nicer days and goes to the river when it's blowing a gale on the lough.
The fashion for over heavy lake boats will die sometime. A tube or 12-14' dinghy suits that angler better on most waters, and possibly a 16'-18' on Corrib or Mask if early season cold weather work will be involved. But when the weather is suitable the tube will catch more fish if you use it cleverly.
There are many bays a 1000 metres wide on Corrib and Mask that are peppered with hundreds of boulders at the waters surface, and impassable to rigid boats. Those bays are full of trout, undisturbed by power anglers, and make wonderful places for tubing if you walk in on the shore with the tube backpacked. The tube can take a big bay of a big lake and fish it well.