It's ok to disagree. I'm in a camp "API + SPA" after my experience. I know as fact that you can greatly increase UI performance this way and build multiple apps (desktop, mobile, web) using single API.
So argument "I just think so" is totally not an argument for me.
If you’re dealing with a lot of custom data for each user they that plays less well into the prerender solutions. But again, it comes down to how best to serve your users’ needs.
I'm old enough to remember when AJAX was supposed to make the web feel faster. It has failed spectacularly at that goal, in fact, whatever potential it may have had. It gave us much better spying on users though, so... thanks?
No, it allows apps to don't rerender whole page on every click, so it works just fine.
So, why?
I'm not so sure you do for many sites. Take something like Reddit for example; I don't think the new SPA redesign is any better than the old template-driven app. In fact, IMHO it's worse in every way. Part of that is just a matter of design and not technical, but part of it is just "SPA hell": CPU goes to 100% on load, takes ages to load stuff, etc.
On the other hand, I find something like FastMail's web UI to be quite pleasant. So it certainly is possible, but I do think it's a lot harder to get an SPA right than it is to get a classic template-driven app right. It's also a lot more complex, which results in all sorts of problems.
I don't think jQuery is the "perfect" way to develop stuff; the lack of structure means things can get messy (we've all seen that), but I'm not convinced that React is the best answer to that (just because A is imperfect doesn't mean B is the answer, a common fallacy in these types of discussions).
I'm not quite sure what the best way is, and perhaps it already exists and I'm unaware of it, but in the meanwhile I prefer to stick with the "KISS" solution. If I look at the websites I really like using then they're all classic "progressive enhancement" ones, and not SPAs (in fact, FastMail is the only exception that I can think of).
Either way, the post was mainly intended as "vanilla JS vs. jQuery", rather than "classic JS vs. modern SPA" (although they're obviously related discussions).