[dmitriid]

> because the web is document-first: HTML and CSS were/are all built-around describing and styling textual content

They were built to display static textual content. Moreover, they were built to display static textual content on 90s-era computers in a single rendering pass. IIRC two-pass rendering didn't appear until some improvements around tables in early 2000s.

For that, yes, they are quire fast. Anything else? Nope.