Nowadays of course we have CPU core swallowing and battery draining JavaScript ads, along with massive JavaScript bloat in general. For the heck of it I just went and had a look at one of my own pages, which runs an HTML5/JS/CSS game, and includes Adsense. It downloaded 633KB of JavaScript. By today's woeful standards that's not even particularly bad. To break it down a bit though, 52KB of it is scripts I use directly, of which 47KB is required for the game. The other ~5KB is FontAwesome, which I use for icons on the menu buttons. The other 581K? Well, Adsense itself is also fairly small (about 35K for two scripts), which leaves the rest - the vast majority - which is loaded by the ads themselves.
Like you, I've come to realise that it wasn't the tool/platform, but the people building for it. Clearly the best developers are not building ads. It feels like there should be some scope for disruption here.