But no substantial modern application can possibly be built without them.

I can see that using modules could avoid the need for compilation.

That's certainly false, since substantial applications predate React, Angular, svelte, etc.

But you have a point. Steve Yegge once wrote that his company wanted to write a word processor in assembly and it seemed like a good idea at first, but then it was like drawing a straight line 100m long using only 2mm line-segments. The major purpose of these libraries is to increase the "length of the line-segments" to something more consistent with the distance you want to cover. The question is whether or not their exists a unit of abstraction in raw js/html that serves this same purpose. E.g. it's a demonstration proof.

Working on it.

Check out Firefox.