If I understand it is not privacy preserving with regard to you and the aggregator but it is preserving with regard to you and the ad agency.

Only if you redefine privacy. I don't want any of my information being leaked.

It is plausible for example that you could form a statistical cohort around people that work in an organization and determine that they have become interested in a topic that reveals internal plans.

Even as an individual, I can only see more accurate modeling of my interests as a tool to be used against me. I do not consent to sharing those correlations. They are private.

This feature isn't modelling your interests. It's letting advertisers get insight into the performance of their ad campaigns without tracking individual users.

The ad agency is only able to see: their add (y), published on source z, led to x conversions, over a period of time (p).