Sorry, my previous comment was probably overly dismissive. I'd argue that developers and users of the F-35 already understand that stealth gains are not permanent. Countries and military organizations that purchased the F-35 definitely hope that the stealth advances last longer than 2025, but they will pay for improvements, new planes, and new tech long before 2070. It seems comically naïve for them to take claims of "2070" at face value without verifying, but that's just conjecture on my part.
Is it? The B-52 has now been in service for 69 years. 50 years is certainly not impossible.
The trade-offs made for stealth are beyond the plane itself, the entirety of US military strategy (and even diplomacy to some extent) is deeply affected by a stealth-focused air-power strategy.
As for stealth advances beyond 2025, I don't see it personally. As long as your doctrine requires you to fly your planes over enemy radars, there's not much you can when the wavelength of the enemy radar is bigger than most features in your plane. It's a physical limit as solid as conservation of energy.
I don't work in radar/military stealth, but my argument isn't that you're wrong about any of your technical claims. Rather, my argument is that the F-35 was designed and purchased by people who are at least as aware of those technical details as you are. This is an assumption, but I don't think it's a huge one. As a nitpick, the F-35 may still be operational in 50 years, just as the B-52 is operational today. The question is whether its stealth will still be useful, not whether it can get airborne. Nobody is using the B-52 for its stealth anymore (happy to be proven wrong), and the decision to lean on the F-35's stealth capabilities for 50 years won't simply be "The B-52 has been running for 69 years, nice!"
If stealth isn't very helpful, why would you fly the slow and expensive F-35? I don't really understand it.
I'm sure the people behind the F-35 were aware of these technical factors, maybe not the extent of Russian/Chinese investment though, but I don't think that their interests were anything beyond making as much money out of maintenance as possible.
As for the people making the purchases, many of them do think that the F-35 made the wrong tradeoffs and a lot of them are pushing for a plane that would fulfill the same role as the F-35 was designed for but with a very different set of tradeoffs.
