> a single component outweighing an entire app feels fundamentally broken.

I think this is an overly dramatic take. Of course react has a fixed overhead. If all you're deploying is the single button, then that overhead is for no benefit. But the overhead gets amortized over your entire app, which most likely has thousands of components. This is like a microbenchmark which only measures the static overhead. Not indicative of a real app.

There's an entire cottage industry of "react" but smaller frameworks out there. Somehow, none of them have caught on.

Preact is the one I'd go for if I wanted a smaller react because it's quite mature and it provides the same API.