As a web dev, I agree 100%. It's a mess.
> That's not a problem, but a very big plus.
...but if your business need/use case is to port with your existing web app to the desktop with minimal fuss (and you're willing to sacrifice UX), this in no way helps (unlike Electron). If you're going to have to manually rewrite everything for the desktop anyway, why would you want to do it in the DOM, using an older HTML version, a CSS subset, and a somewhat-compatible JS-lookalike? Why wouldn't you just write it in a desktop-native UI kit?
I pretty much understand this point and see that Electron help. I would definitely write desktop-native UI, maybe just because I prefer it. And in large programs it might be somewhat expensive. But on the other hand, I found writing QT programs to be much easier than messing with web stacks.
IMO React is a response to a problem that not all websites have (complex state-dependent nested UIs). At a certain level of complexity it's worth it, at another level it's necessary, beyond that it's insufficient... but below that it can totally be unnecessary and more pain than it's worth :)
Go with what works for you and your team!
Also, whatever you write won't then be usable in normal browsers. So it's essentially just another cross-platform UI library, with a DSL for the UI parts - of course that's still good enough for many people.