Google being on both the sell and buy sides and the “advantages” of using Google for both were things practitioners just sort of knew and had to live with, like “npm is a mess” and “A/B testing is often more storytelling than rigor“.

I suspect the reason it wasn’t a bigger bombshell is that ad exchanges are hard to understand beyond the surface level “it’s an exchange for ads”, and other ad exchanges were also dirty. Google wasn’t the only one doing questionable things being on both sell and buy sides of transactions:

https://www.businessinsider.com/guardian-takes-legal-action-...

One of the most astounding things I learned in my time in ad tech was just how wide the gulf is between how much the advertiser pays and how much the website owner gets. It’s one to two orders of magnitude difference, mostly made up in fees for all of the platforms and data and other value add in between.