I'm personally not okay with Apple to take a full control on the App Store, but let's admit the reality and think about feasible options; then what would be remedies that Apple doesn't have a good justification against? I think one of the issue is information asymmetricity between Apple and customers.
* For each in-app purchase, Apple MUST explicitly highlights how much commission they're taking.
* For each in-app purchase, Apple MUST allow app developers to show alternative payment options available.
* Apple may review the alternative payment options and reject the app if it is implemented in an obviously unfair way against Apple IAP, but no other reasons. If it is violated, Apple MUST give a clear reason and actionable items to app developers within a reasonable time frame.
This doesn't require any technically complex changes but just gives strictly more information to their customers. If the customers think it's justifiable, then they will continue to use Apple's IAP. If not, they will go to the developer's site. If the alternative is designed to be unfair against Apple, at least they can have a chance to raise an objection. For the rest, let the market decide.
* For each in-app purchase, Apple MUST explicitly highlights how much commission they're taking.
* For each in-app purchase, Apple MUST allow app developers to show alternative payment options available.
* Apple may review the alternative payment options and reject the app if it is implemented in an obviously unfair way against Apple IAP, but no other reasons. If it is violated, Apple MUST give a clear reason and actionable items to app developers within a reasonable time frame.
This doesn't require any technically complex changes but just gives strictly more information to their customers. If the customers think it's justifiable, then they will continue to use Apple's IAP. If not, they will go to the developer's site. If the alternative is designed to be unfair against Apple, at least they can have a chance to raise an objection. For the rest, let the market decide.