Or, in a sentence: you can't claim something is indivisible, and then charge for its pieces separately and at separate times.
Your point is probably that developers and customers are two separate groups, and there's a history of making a thing free to customers (the App Store) while charging vendors (developers) for the privilege.
I just don't see how your "then" follows from your "if" at all! The integration of iOS and the App Store is from a user's perspective. No one seriously believes that Apple is claiming that the two things are literally physically impossible to split up technically. You might as well be arguing that it boggles the mind for the calculator app to be free, but for iCloud storage to cost money!
Except Apple in the court does. That is the exact stance why they cannot allow third party stores and browser engines since those are technically a part of indivisible OS services. Of course, this is obviously BS and inconsistent to many other Apple's business practice, anyway it's their official legal stance in nearly all of its antitrust lawsuits.
Oh, so every iOS users need to understand all the app review policy and TOS before spending their money on iOS ecosystem. Otherwise they cannot complain about what Apple's doing? Customer protection and antitrust regulation don't work like that.
> This is nothing like moving to another city or country.
Why? The main reason of using alternative store is mainly having cheaper apps and contents, usually several cents per each. And you're suggesting that I need to spend ~$1000 upfront cost as well as giving up all the apps and contents that I purchased in iOS? I think it's pretty similar to "moving to other cities", which illustrates how classic monopolist lock-in strategy works.
Instead, what people want, is for users who already own their own phone, to be able to do what they want with it, without an uninvolved 3rd party (Apple) getting in the way of transactions made between the user and the developer.