I think the situation is more nuanced than that.

Of course, the F-35 program was an incredibly expensive mess (litterally the most expensive weapon program of all time), because of conflicting specs, data leaks, political infighting, cost overruns which are the stuff of legend, etc... At some moments, there were certainly reasons to think the whole program would collapse on itself like wet tissue paper.

But there are operational F35 now. 900+ as of 2023, which is 4 time more than the rest of Gen 5 fighters combined. And performance-wise, it is good, especially on the stealth & avionics parts. On the other side, the J-20 is largely unproven (probably a decent design, but not as good), and the Su-57 is a bunch of glorified prototypes.

Now sure, cost is high, maintenance is time-consuming, availability somewhat below target, but it's not particularly surprising for high-performance equipment. It may fall short of the ambition of the program on the cost part, but by itself it's a dangerous and fully operational fighter.

Anyone that says that has no idea what they're talking about lol, the F-35 is completely unmatched in terms of multirole aircraft (along with the F-22 for a more fighter-focused role) and likely will only be surpassed with gen 6 aircraft.

The SU-57 and practically any "modern" Russian aircraft are complete jokes that will fall apart with 2 seconds of airtime, and the J-20 and a majority of Chinese aircraft are cheap imitations of western (mainly American) technology which although much more capable than Russian aircraft, still fall behind a lot due to the corruption/authoritarianism in the Chinese military & government absolutely crumpling any hope of having actually competitive engineering & building.

European aircraft aren't even worth considering as competition either (although are far superior to the previous 2 nations' mentioned, in most cases). Eurofighters are just another one of the projects European nations had that was plagued by issues from the fact that it was multiple parties with differing requirements/interests/goals trying to develop something. Gripens are less effective budget alternatives to American gen 4 fighters. Etc. Etc.

The combined capabilities in technology, resources/wealth, and pool of experienced/intelligent engineers that the US has at its disposal makes it extremely hard to even dream of touching their capabilities when it comes to aircraft. Even with ground vehicles, the only real competition is Germany... but German armed forces are kind of in a state of disrepair right now, they've really neglected their military. It's really only the defense companies like Rheinmetall and KNDS which can be pointed to as successful currently.

Europe has a long way to go to compete with American military aircraft. Right now the US just has so much more experience and knowledge when it comes to fighter jets & more modern technologies present in said jets. It'd require a lot more investment in aerospace engineering and technology as a whole really, not just when it comes to aerospace. And Europe is currently even more desperate for tech workers than the US atm afaik.

We didn't even roll it out for testing at VX squadrons until like 2018, and it's biggest claim to infamy is just being on the R&D line for like 25 years.