I agree, people often underestimate the complexity of a browser and its ecosystem. Yet, I find it valuable that people question the merit of all these additional layers, especially those added by JS frameworks. What do they yield? Do they allow you to more quickly develop an application? Are the applications better than before, by any metric?

I'm pretty sceptical because coming from real-time & desktop programs, I find UX on most web apps I use leaves a lot to be desired: I regularly see state inconsistencies when I go back & forward in my browser, I cause race conditions by quickly editing fields, fight with input validation missing my input, and just die a slow death because the page is just slow. I would have assumed that frameworks existed to remove all these burdens from developers. Yet that such issues persist so stubbornly for over a decade shows to me that somehow, even such simple and recurring tasks as providing and validating forms are not properly solved by those frameworks (or the field is full of people that don't know how to use them properly? Then, why is using them correctly not easier?).