> Having a "build and bundle" step is just the webdev version of compiling developer-friendly code (React and frameworks) into the "lowest common denominator" code of browser-parseable HTML + JS.

One problem is that for all the building and bundling webdevs do, only a few very recent frameworks (Svelte and SolidJS) can even manage to compile into something that even approximates "plain vanilla", progressively-enhanced JS on the client. And use of these is still the exception rather than the rule.