For me, I think the open question is can they deny 3rd party app stores or side-loading apps. Then, we get into the "Microsoft installing IE by default" fight. How can a 3rd party app store compete? (I don't have an answer)
This is somewhat the basis of the lawsuit that actually brought this out.
The accusation is (iirc): Google has backroom deals with OEMs to prevent them from having any market installed by default except for Google Play. This is what stopped Epic from continuing with their own mobile market idea, as no OEMs would agree due to this.
The European Union's Digital Markets Act finds that pretty easy.
The DMA will let them charge 100% fees if they want, it just won't allow them to be the only store on the platform to force people to pay that fee.
If they are a monopoly or duopoly or cartel it is very easy to argue against that.