Apple could already do things with the App Store without needing to agree to something to get Apple to let Apple do App Store things.
Apple is not going to sue themselves for being in breach.
etc.
Just because there's e.g. a license agreement doesn't mean you need to agree to something, if you are somehow otherwise authorized to do the thing. E.g. fair use, or you have a pre-existing right or ownership, or whatever.
This is a common tech enthusiast fallacy: thinking that law is code. So there must be some "if app published, there must be a developer account, and if the developer account violates the rule the app must be removed". It just doesn't work that way.
Apple has contracts with third parties to allow them to distribute apps in Apple's App Store. That's it.
What does fair even mean here? Ensuring the advantages of vertical integration can’t be enjoyed by users?
It's not the worst idea I've heard, tbh.
And it’s a pretty bad idea. It basically means that no apps that ship with an OS can be available in the store.