> Last time I've used a JS heavy site the UX was just utterly awful.
That's an issue with the web site, not the underlying technology.
> […] people would have eventually fixed the bad parts of flash.
The Flash plugin was a closed-source component. (Various attempts were made at open-source substitutes, but none ever reached a fully usable state.) The only people who could have "fixed the bad parts of Flash" were Adobe employees, and they didn't.
That's an issue with the web site, not the underlying technology.
> […] people would have eventually fixed the bad parts of flash.
The Flash plugin was a closed-source component. (Various attempts were made at open-source substitutes, but none ever reached a fully usable state.) The only people who could have "fixed the bad parts of Flash" were Adobe employees, and they didn't.