The traditional way to handle this in the offline world is with ratings agencies like Nielsen. This is the thing where they try to figure out how many people are watching each TV channel or who read a given paper.

The problem is, this requires the readings agency to build up a representative panel of people, and track their behavior. This is pretty coarse, but it works in a relatively centralized world like traditional TV where there are only a few dozen channels. On the web, however, people visit so many different sites that the panel would either have to be extremely large or you would only be able to generate reasonable ratings for the largest sites, probably both. This would be yet another force pushing hard toward internet consolidation.

Another option is that you could somehow build a new technology into browsers with some sort of privacy preserving API. I used to work in this area [1] but I am pessimistic about it: it's very hard (and may not be possible) to build something that gets all three of (a) minimal load on the users browser (b) actually useful fraud detection and (c) sufficiently private (with a separate question of whether usage would require consent under GDPR).

[1] https://privacysandbox.com/open-web/