I wrote not so basic CRUD application that uses HTML and vanilla javascript. I don't even minify the javascript. That website loads significantly faster than all the other websites I have made.

This is obvious and not an interesting observation.

The question is how to get a good and efficient dev experience while also preserving that level of speed.

AI has now made that question mostly irrelevant, since it can generate and rapidly edit vanilla webpages without a framework to make the DX better.