Huh? Cop-out? Netflix users have had to subscribe via the Netflix site the past few years. Doesn't seem to have hurt Netflix one bit. Seems Apple users figured out how to keep Netflix without going through Apple. Why doesn't Spotify do the same? Both companies are at the top of their industries.It's cosmically dumb to have a system that fundamentally requires payment through only their environment on one hand, and the other hand disallows any possible mention, link, or reference of alternative payment possibilities. That's monopolistic behavior.
And the argument of "the other guys do it" is also (edit) kind of a cop out. They've simply done it because it worked at the time. Some of these services have evolved to become "the biggest" over the entire ecosystem evolution of both the apple app store and their streaming systems. Apple has never, ever allowed even the mention of paying outside of their bubble or even mentioning how to pay outside of their bubble.
This argument always gets cyclical too. Sure, people have the choice of Apple or Android. But do they really? Once you're on an Apple, you literally have one store. It's not like you'll throw your phone away and go get an Android. You are, in very much reality, locked in to that one store. And that one store's rules even disallow devs, customers, anyone to even know that you can pay for something via alternate methods. It's the Apple Way or No Way.
So even citing your example, if Netflix had existed this whole time with a banner inside the app stating very explicitly "To subscribe to our service, please go to netflix.com and pay there!" you'd have a valid argument. And that would be an amazingly easy answer to this. But no. Not allowed. Not even that. Even without a link.
Like mere knowledge of a different payment system (apps can't even mention how to pay on their own sites) is somehow protecting Apple users? No. That's why this is so dumb, and obvious that Apple only takes this stance to drive more money and payment processing through the Apple app store -- it's purely for money, not security.
As for Apple or Android the choice is there and it's not difficult to switch to either unless one is a green bubble fanatic.