I hear you. But this battle is lost for a long time, isn't it? You already know, that if you allow CSS things will happen.
I would personally not do this if browsers would have sensible defaults, but IMO they don't. Mostly it is a matter of backward compatibility.
Also I'm using font:menu so theoretically the same as your browser is using. Depending on your browser/OS you can change the font for all, not ideal, but doable. Similar to how every browser has different settings for your preferred fonts. But in Firefox for example you can deselect "Allow pages to choose their own fonts, instead of your selections above" and you're done.
I'm saying all this as a person wanting to implement a modern html-only browser to make all those obnoxious stylesheets go away.
I don't see why you'd think font:menu is appropriate for the general body of web content. Menus are a UI element that normally contain just a few isolated words or very short phrases. Recognizing words in such a context is not the same as reading textual content on a page. A font chosen for one may not be well suited to the other.
If your issue is that many browsers default to a serif font, and you really dislike that, maybe setting font-family:sans-serif would be better? At least that's intended to be suitable for content, rather than UI.
I would personally not do this if browsers would have sensible defaults, but IMO they don't. Mostly it is a matter of backward compatibility.
Also I'm using font:menu so theoretically the same as your browser is using. Depending on your browser/OS you can change the font for all, not ideal, but doable. Similar to how every browser has different settings for your preferred fonts. But in Firefox for example you can deselect "Allow pages to choose their own fonts, instead of your selections above" and you're done.
I'm saying all this as a person wanting to implement a modern html-only browser to make all those obnoxious stylesheets go away.