At that point consumers would be free to make a choice to switch away from Apple if they value their privacy enough. The problem right now is that Apple is 'abusing' the fact that privacy-aware consumers are drawn to their platform to charge onerous fees to app developers. They're leveraging their (de facto) monopoly on high-end mobile privacy-aware devices to restrict competition in mobile app fee charging. It's that business practice that's wrong - having a monopoly is fine so long as you don't start using your monopoly position to make money from people who are your customers for some other business.

Microsoft fell foul of this in the early 2000s. It wasn't their monopoly on desktop PC OSs that lost them an anti-trust case. It was the fact they used their monopoly on Windows to push users into adopting IE. They abused their monopoly position. That's the problem.