Earlier quoted context omitted.
PHP has as much client-side rendering as React SSR does. I think the sleight of hand that is happening right now, and that gets people a little confused, is that React is shaping up to be this thing that handles both front and the backend where other solutions can't do that. Sure – but it does that by overloading and complicating what React once was (neither of which per-se negative, I think it's just an apt descript…
React borrowed these concepts from Solid, SvelteKit, and Remix. Not that there’s anything wrong with that. It’s pushing things forward. (And by forward, I mean, yes, also a little backward. We had server-side dominance with php, etc., then frontend-only with Vue/React… Now we finally get to serve our cake and consume it, too.) I sometimes hear snarky comments about the proliferation of all these frameworks. But here…
The new frameworks were poised to eat React's lunch, they knew it, and they needed something quick to hold back the rising tide.
They may succeed, but only due to inertia, not a better/cleaner solution.