I think there needs to be some distinction between apps that are the main product (or close to it) and apps that support another product (like there is npo point to having the app by itself, you should already have gotten the product/account before downloading the app). I don't know too much about Apple's rules to know if they use that criteria, but it makes sense to me. An app to manage your Tesla makes no sense unl…
There's been couple of times when I've eaten the markup that comes with paying through Apple simply because that means that I can go into my iTunes subscriptions page, hit the "stop" button on it, and it's done. No buried unsubscribe links, no "tell us why you're leaving" quiz, no disputing charges on my card. It's done and over and I don't ever have to think about it again.
If third-party payment services become the norm on the App Store, I expect a steep decline in quality of unsubscribe experiences across the board.