The problem is people treat HTML, CSS, and JavaScript like they are separate languages. They should be treated collectively like bytecode/binary and almost no one should need to know more than they exist, a compiler should be what's writing web output.
Are you saying that content and layout _should_ always remain combined?
I accept that we come to this understanding through our early introduction to language, writing and art. Most people intuitively link structure and presentation when they compose content.
Separating them is incredibly useful. You can see this at a really basic level, in plain text. Lay out a single long paragraph of plain text into lines of max 80 chars, and then insert a word. The layout goes completely wrong and if you don't have tools to help you, you spend ridiculous amounts of time realigning the text. The line-length algorithm you're following (or using) is __totally__ separate from the content. HTML and CSS are this, scaled up to allow fine grained annotation and control of both semantics and presentation, independently.
XSLT is there, chrome supports it, but no progressive rendering, or support of modern XSLT versions.
Basically, Google wants to kill XSLT, and normal web in favour of Javascript, and WASM based web. Why? They don't want people to turn off javascripts, so they can show more ads, and competitors cannot get an easier job making google.com alternative.