[stickfigure]

While these terms are fuzzy, JSX has less in common with the template languages we used in the 2000s and more in common with interface builder languages like XUL. The experience is assembling components on a screen rather than generating HTML. Despite all the plumbing complexity, React/JSX (and Angular et al) feels fairly familiar to GUI developers from the 90s like me.

I agree with you that "client side app being rendered server side then hydrated" is pretty weird. I also don't think this is the future of the web but rather a holdover from the previous HTML-based era. It may never go away; after all, lots of content is very well suited to simple HTML.