As far as I can tell it is the European monopoly model. (My info all comes from Stratechery's coverage - errors are all mine.)
Monopoly regulators look at consumer harm, with US regulators focusing on price. Increasing prices are seen as monopoly power, and that is what they coordinate around. That for example (as the article notes) is why Facebook, Google etc are not seen as monopolies because they charge consumers zero.
Conversely the EU approach is looking at supply - eg can there be new entrants? The Google shopping stuff was an issue because it is way harder to be a new entrant if Google (where many find the sites) demotes or hides the new comer. Facebook is an issue because it is impractical to start a new social network. A new network has to get users to re-do their social graph - they can't just get a copy from Facebook. GDPR making more sense now?
With the "supply" view on, you can see how network effects keep making Amazon more and more efficient (economies of scale) while also making it increasingly difficult for there to be competitors. Their size also lets them impose their own policies (eg see ebooks over the years).