How can I generate pages with dynamic content easily? Ideally with absolute minimal dependencies.
You still need Ajax (at least) for truly dynamic content. The bad news is that Ajax requires client-side JS. The good news is minimal Ajax functionality only takes about 30 lines of pure Javascript. The bad news is you will need to write those 30 lines yourself because every JS library is at least 100x bigger than that and packed with cruft you don't need.
My advice is to pretend React doesn't exist, learn Javascript, and write just the Javascript you need and no more.
With SSR, you need some component that's aware of every change, and that triggers those re-renders at sensible times (every render takes server resources). This all feels messy, compared to rendering just-in-time on the client-side.
What part of it do you think is bad for usability or accessibility?
If you want to build something that's nice for humans and machines, look up best practices for this sort of thing - plenty of information is widely available on how to build things in usable and accessible ways (and it's simpler to do it correctly than to use these 'hack'-like workarounds anyway!)