There were other things like the "Ajax" (remember that word?) API, but that one's also been matched by a native API (fetch())
> keeping state within the DOM has fallen out of favor of more comprehensible state management inside of JS
Not everything needs a whole reactive templating library. There's absolutely still a usecase for mostly-static sites to do imperative DOM manipulation.
The usecase for jQuery itself these days is dodgier, since as you point out most of its big features are native now. It should still help with browser compatibility (not necessary for modern-ish browsers, but many sites don't want to limit themselves to modern-ish browsers), its APIs are arguably still a little nicer in some places, and it does have a significant ecosystem of plugins so there's probably some value in having that stuff integrate together. But personally I would have a hard time justifying a whole library just for slightly nicer APIs unless I was doing something significantly complicated, and at that point I would just use React.
> keeping state within the DOM has fallen out of favor of more comprehensible state management inside of JS
Not everything needs a whole reactive templating library. There's absolutely still a usecase for mostly-static sites to do imperative DOM manipulation.
The usecase for jQuery itself these days is dodgier, since as you point out most of its big features are native now. It should still help with browser compatibility (not necessary for modern-ish browsers, but many sites don't want to limit themselves to modern-ish browsers), its APIs are arguably still a little nicer in some places, and it does have a significant ecosystem of plugins so there's probably some value in having that stuff integrate together. But personally I would have a hard time justifying a whole library just for slightly nicer APIs unless I was doing something significantly complicated, and at that point I would just use React.