So yes, lots of people buy iPhones exactly because if Apples iron grip.
That's incredibly disingenuous and you're either being dishonest or ignorant. The 30% is for sales made on Apple's platform. Developers can absolutely make sales without giving Apple a cut as long as they don't use Apple's infrastructure or platform. You can have people purchase things for your app as long as you don't attempt to offer in-app purchases that circumvent the App Store.
It would be like you using AOL and only being able to view the channels that AOL offered (which is exactly what it was). Apple has no authority to tell you what you can do with your device once you've purchased it but you also don't have the authority or the right to demand that Apple service your device if you jailbreak it or mod it.
This is literally the exact same situation as Xbox and PS4. Xbox doesn't allow people to play PS4 games on an Xbox. Is that anti-competitive? Is that anti-consumer? Is that Xbox having absolute authority over what you can do on your Xbox? Get out of here with that nonsense.
I know, I know, people who bought iPhones knew what they were buying into.