I don't think this article explains it well. Google sells ad space on behalf of the publishers and also sells the ads on behalf of the advertisers. It also runs the auction that places the ads into the ad space. See this graphic https://images.app.goo.gl/ADx5xrAnWNicgoFu7 . Parts of this can definately be broken up without destroying Google.
And crucially, there are leaked emails, other evidence that demonstrate (at the very least historical and occasional) corruption of this dual- (multi?) agency arrangement. Among the allegations: The Google ad exchange favored its own platforms, limiting the ability of other exchanges to compete fairly in bidding for ad inventory. https://www.justice.gov/archives/opa/pr/justice-department-s... In limiting the number o…
Note that this link says absolutely nothing to support the sentence before it. Which isn't a surprise given that limiting the number of bidders could hardly drive the prices those bidders are paying up. But the issue isn't even mentioned.