There is a gaping chasm between a website that needs some Vanilla JS and light interactivity, to the point where a framework like React is a necessity though. Like if all you're using React for is to pop open a side menu or render some lists, you've taken on a boatload of tooling overhead for pretty minimal gain. Performance isn't going to be the problem there, the issue is having to maintain a relatively cumbersome tooling ecosystem for the site. That's not a contrived example either, I've seen plenty of that going on.