I linked a computerphile video explaining how HTML ended up as a loose defined language, meaning browsers will often struggle to render something.

I think it's part of the whole thing, HTML is too permissive, and it also will make rendering slower. If HTML was better defined from the ground up, rendering would also be faster. The sites I visited were not really JS intensive. JS is also a problem for webpages.

Anyway I hate HTML/CSS/JS in general for all those reasons. Parsing text is already painful, why do it each time you visit a webpage?