> But as much as I hate to admit it, it is very difficult to build something functional today with plain HTML and no/minimal JS.
I would certainly agree that using a little JS can get you further than just HTML. But I think that a plain HTML page is far more pleasant to use (and thus, functional) than the JS monstrosities that dominate the Web today. There's a reason people use the NoScript addon: because a whole lot of website designers use JS in ways that make the experience a ton worse for the user.
It's not an either/or. Modern Javascript is actually really nice to write and use, and you can write it in a tight, minimal way that doesn't bloat the page or slow it down.
Of course you can, but most people still opt to pull in a whole framework (React) or heavy library (jQuery) just to achieve what's essentially a few XMLHttpRequests and some DOM changes.
I would certainly agree that using a little JS can get you further than just HTML. But I think that a plain HTML page is far more pleasant to use (and thus, functional) than the JS monstrosities that dominate the Web today. There's a reason people use the NoScript addon: because a whole lot of website designers use JS in ways that make the experience a ton worse for the user.