Consider Spotify vs Apple music. If Spotify has to charge X + 30% to subscriber's on iPhone in order to make X then they absolutely can't compete on price if Apple simply charges X.
You're just making things up. Apple has explicit exceptions for multi platform subscriptions. The only condition they require is that developers should not cripple the iOS app by removing the ability to create an account from within the app (which means your app essentially has to offer in app purchases as a valid way of obtaining a subscription).
If users want they can create an account on Mac (or even on iOS Safari) and set up a subscription with lower fees outside the app and then use it inside the app.
People can easily use the Netflix accounts they created on their Mac on iOS with no extra charge.
What's not allowed is making an iOS app where you are shown a login screen but no way of creating an account from within inside the app, which forces you to use a separate platform to create the account. The idea is that an iPhone or iPad should be a standalone device and not require the help of another platform or device to do basic things like create an account.
Can you create a netflix account within the app on iOS? I thought they specifically had an exception for "reader apps" (and Netflix somehow fell in that category).
It's not relevant. The cut taken is not the point. It's that the app store is the only avenue onto an iOS device. EVERY OTHER meaningful computing platform (that is, not solely a gaming device) has multiple avenues to acquire and install software. Not iOS, and that's the issue.
I don't know why I keep expecting users here to understand this. It's not going to happen.
What about Chrome OS? Only some chromebooks have unlocked bootloaders, otherwise there is no way to install new software besides web apps or browser extensions.
Consider Spotify vs Apple music. If Spotify has to charge X + 30% to subscriber's on iPhone in order to make X then they absolutely can't compete on price if Apple simply charges X.