I mean, the broad problem is web performance. I think that client-side rendering is a red herring, and really not the main problem. I think part of that issue is that developers don't spend as much time optimizing performance, because it's less clearly necessary up front.
Web in particular is very hard to optimize for performance just because of its inherent platform limitations. For applications, people expect as-good-as-desktop. But you can't just download a big .exe and install it -- you have to transfer everything over the wire, which is obviously very expensive. So the big optimizations are reducing how much you need to do that. In apps where people click to new pages and do server-roundtrips for interactive data constantly, you can reduce the amount of time your blocked by caching stuff in the browser. For pages which transfer a lot of data, you must use webpack and similar tools to compress and optimize the various bundles.
The second issue is that when people experience slow and annoying websites, it's normally because of ridiculous ad tracking and subscription popups, which are things most web devs don't really care for. But this is also how the web is funded, so you can't just wish it all away. But this is completely unrelated to client-side rendering frameworks.
Another point is it's not like servers are automatically fast. Sure, more powerful than client computers, but also serving many times more people at once. You'll have to do performance optimizations for servers too.
So my main point is that 1. client-side rendering being slow is usually a red herring. and 2. with any site, you should be optimizing performance. That includes both client and server, both of which can be tricky to optimize
And I do think baseline expectations are higher. For example, on old.reddit.com, when I open a post, it opens a new page. When I go back to the post list, the whole page reloads, which takes time (and I'm on a gigabit network). It's a lot faster in new Reddit, where everything happens on the client. At the same time, I'll certainly agree that it's very poorly optimized in many cases. I think there are some memory leaks. It's a solvable problem, though. It's not bad because it's using React; it's bad because they haven't taken the time to optimize its performance.
And talking about GitHub. The new client-side nav is a lot faster for navigating around a codebase than the full page reloads it used to do. It makes sense, that's a huge part of the page you can just leave there. It's a performance optimization to use more client-side rendering in this case, pretty clearly. Fewer round trips to the server (very slow), less data to fetch overall because half the stuff on the page doesn't need to change... etc.
And products like Google Sheets and Google Docs have also really pushed hard on client-side interactive features that were not common 10+ years ago, but are more common today.
And talking about hacker news... here are some problems hacker news has that modern websites typically don't have:
- Form submission weirdness, particularly around the back button
- Have to go to a new page and reload the old page when writing/editing a comment. More round trips to the server.
- Styles are poorly optimized for visibility on both desktop and mobile.
- On mobile, touch targets are very small.
- Form markup is limited and opaque (e.g. most people expect to have a toolbar for rich text options).