I've been involved in quite a lot of usability testing and I'm often positively surprised by the responses. Which is why I'm sort of skeptical when reading such claims. Also because I think user experience overall has improved, by a lot, the standards now are so much higher than the used to be.

I think it almost always comes down to one thing: Can people achieve the thing they want to achieve in a somewhat efficient way?

If the answer is yes there is lots of tolerance for all sorts of crap before people experience it in a negative way.

That means managing the experience. As example a multi minute upload process can be totally fine if handled properly, a .5s delay on an input can make it unusable. My point being; reality is a lot more nuanced than the blanket "it all sucks, and performance is everything" statement, and personally I don't think it's helpful. Unless we can actually look at metrics and assess their importance and how we can address them.

Don't get me wrong; we should absolutely keep trying to improve, especially crafting well made usable interfaces that are a delight to use. Performance is certainly very important, but it's not the be all end all of user experience and atm wrongly used to justify silly points why [my fav framework] is so much better than React.