OK, but right now as a user I have a choice: I can choose an ecosystem supported in part by a 30% tax on apps, or I can choose an ecosystem supported mainly by advertising. If Apple is forced to allow other stores, I lose that choice.
Furthermore, a lot of the things Apple forces on apps really are for my benefit: Take the way they banned Facebook for working around their prohibition on running in the background. They can say, "If you want to access this market, you will follow these rules." If Apple is forced to allow other app stores, then not only Epic and Spotify can say, "We only install on this other store that allows us to sell subscriptions without the 30% tax", then Facebook and others will also be able to say, "We only install on this other store that lets us spy on you."
One again: At the moment, as a consumer, I can choose to say, "I prefer Apple to negotiate on my behalf" or, "I'll go with Android, where I can install third-party stores". If Apple is forced to open up, I won't have that choice any more.