Whoever owns the device can do what they want with it, Apple cannot tell you what you're allowed to do with your phone. You're making up a scenario in your head.

This goes both ways - when Apple produces a phone, they own it and they're also free to load whatever software they want onto it. They then enter into voluntary transactions with others, in which the ownership of the phone is transferred along with the right to load whatever software is desired.

If you can't figure out how to load your desired software onto an iPhone, don't buy one. But it's certainly not Apples problem at that point since, as you said, they no longer have a right to any say in how that device is used, and thus also give up any responsibilities you seem to desire.