Can't the big sites negotiate directly with advertisers? I thought I read somewhere that the New York Times does this. In that case, why bother with the bloat of ad networks and their monstrous JavaScripts and other garbage?
If it's (as you say) good riddance to the small, scammy sites then I think it's the medium-sized sites which will really have a problem. Not big enough to negotiate directly, not small enough to disappear overnight.
Except a few very rare cases, ad networks can statistically deliver a far more effective ad than a manually curated ad.
The network also has the infrastructure in place to track the user all the way from the ad click to completing a purchase, potentially across many devices or even in a physical store. They use those numbers to demonstrate their value with hard figures rather than marketing fluff.
