The basis for my claims about the subject is my knowledge of computing and development in general. I dipped my toes into iOS dev a few times and there's nothing that seemed to set it apart from any other SDK situation beyond Apple's restrictions, at least nothing that would make my claim outlandish.
Core device apis yes, everything else, maybe not?
I think we could roll our own UI - I think we can roll our own payment systems - I think we could roll our own media display.
For the primary iOS app I work on I need vulkan, gps, touches camera, sound, and phone rotation. (And standard os services)
I don’t need anything else.