> Imagine a world where you just had drawing and input handling primitives on the web. You wouldn't invent the DOM and then something like React to wrangle it that's for damn sure.

I think this is a really good thought experiment and that you are right - we wouldn't end up with the DOM if we started from scratch. It's a pretty bad local optima resulting from decades of legacy cruft. However, I do think react is closer to that ideal than the DOM.