I'm confused how this is a monopoly, is it just the "if we define a market as Google ads, then Google has a monopoly problem"? Like defining iOS apps as a market (and somehow failed)? Even if they play games with the auctions to keep the price up, at the end of the day X company is spending $5 per thousand clicks (or whatever) because they think it's worth it. Google can charge whatever they want, they run the platfo…
There is no other way to get an ad on sites that use Google Ads, just as there's no other way to get an app on iOS. These seem to be perfectly parallel to me: in either case you can pay a company to get access to their user base or you can choose to not pay that company to get access to their users. But if you make that choice, in either case you're locked out of a large market.
I agree with you that there's a strong argument to be made that the cases should have been decided the same way, but I also think they made the right call with Apple, so that leaves me reevaluating my gut instinct on this one.