Apple's commission could very well be on the basis that they create and maintain the APIs, libraries, and GPU that enable the developers to distribute on iOS at all.
Then charge people for it. Developers are the people enabling and exposing this functionality, not the ones using it. Apple gives away the Apple services and iCloud functionality to all of their users - if these are expensive then it makes no sense to charge the developers for it. By your logic, this "expensive OS" theory should be amortized by an iOS subscription service - but it's not. Apple chooses to develop iOS, it is not democratically compensated somehow by the success of the App Store.
Orwell himself warned of the "perversions to which a centralised economy is liable", maybe the company that spoofed 1984 should take it to heart. The optics of the world's largest business doubling-down on their right to control what their customers use is a bit dystopian, if I say so myself.
They can use similar a similar pricing for push notifications which is offered by other providers. Would be perfectly fair.
If it works the same way as it does on Android then they can’t really demand you to share your revenue .