Oh absolutely, that ship has long since sailed, it's just me lamenting a world that could have been if something closer to simple.css or tufte-css had been the norm.
Though with "reader mode" becoming more popular I wonder if there's a place for a browser with more opinionated defaults.
There's a lot of sites between pure html and modern css. "Simply" rendering things differently would definitely break a lot of sites. Just imagine if browsers started defaulting to *{box-sizing: border-box;}.