You're not wrong but we've never really tried the combination of modern CSS with no JS. It could produce elegant designs that load really fast... or ad-filled slop but declarative.

Yes to the modern CSS. To go as far back as suggested would mean using frames again and table based layouts with 1x1 invisible gifs to use for spacing layouts. Never again!

Ads don’t work nearly as well without JavaScript for adtech. They’re basically limited to static banners and text ads as well as sponsorships.