Well yeah. In this case I'm afraid you're wrong. You don't violate patents or copyrights by making something that's compatible with a copyrighted/patented work, insofar as you don't violate the copyright/patent.
Having your code call an API is not a copyright violation.
It’s not possible to call Apple’s APIs without their SDK and the SDK is closed source and distributed with the App.
Apple is within its rights to request compensation. You could try to reverse engineer them, but then Apple might: 1. Sue for copyright infringement. 2. Continually change iOS so syscalls require a signed certificate in the SDK.
It’s effectively impossible to get around their copyrights on iOS and as such it’s not very different to the licensing and compensation of the Unreal Engine.
All this said, I really would prefer Apple to document and encourage Linux on the iPhone as a secondary boot option (along with a voiding of the device’s warranty). That way iOS would be locked down but other OSs on the iPhone would not need to be.
Or are you arguing in an ethical sense?