I strongly suspect that 80-90% of the bloat and slowness is due to the ad/tracking parts. Yes, there's bloat with modern web/js tooling but even React and Angular (I think the heaviest of the modern bunch) are on the order of hundreds of kbs gzipped over the wire, and the benefit they give is better ux. "Old web" was fast/bare-html but not great for nontrivial ux.
And I sadly don't know either what else apart from whining and moaning the average user could do.