You’re conflating some ideas here. A marketplace owner always has “dominant market power” over the market they own. That’s the nature of marketplace, the owner gets to set certain rules like the types of payments accepted at the marketplace, because that is literally the job of a marketplace.
Google also has dominant market share, since their App Store is the best for android, but that’s legal (keep in mind Amazon, another $1tn company actively competes in this space) - the government does not want to force consumers to use worse app stores. Competition for the sake of competition is not pro consumer.
What Google probably isn’t doing (and what is illegal) is using its OS market power to crowd out other app marketplaces. As mentioned above Amazon meaningfully competes in this space. The closes you could get there is Google doesn’t publish its own apps to other app marketplaces, but that’s likely not across the bar of anti-competition.
