Old fashioned ads were targeted based on the thing they were attached to. For instance, if you read the sports pages of a newspaper sold in your city, you probably got ads of presumed interest to people in your city who are interested in sports.
To restore that kind of system, you would need to focus on those kinds of issues: making advertising first party, distinguishing between parts of a site without distinguishing between users.
But once you've done that, you're still left with first parties that can spy on you and use that data in non-advertising ways, or even presumably for direct marketing (if you have some kind of an account).
I think it's better to focus on the surveillance. If they can't surveil you, then they can't use surveillance advertising. As you point out, focusing on leaks is irrelevant because I don't really feel better that only Google knows everything about me. Focusing on advertising doesn't stop them collecting data, it just limits how they can use it. If we don't want the data to exist, collecting it should be prohibited.
Doesn't this just consolidate power among FAAG even more? They can pay these fines and they don't often leak data- if ever. That's another thing- define leaking data. Sharing with 3rd parties? It's vague enough for them to beat that in court.
We do somehow need to get back to advertising the old fashioned way rather than this surveillance capitalism arms-race.