But users can pay how they wish, if Spotify didn't mind the 30%/15% cut. Spotify simply can't direct users to use their website to use an alternative payment system. I think that is a very reasonable policy for an app store, as it protects its users from poorly implemented financial info handling and scams.
I agree that Apple's article is more hostile than it needed to be, but it is only in response to an unreasonable attack by Spotify on Apple's IAP policies.
Regarding the walled-garden App Store policies of Apple, it's not friendly to enthusiasts and some developers, but it is good for most Apple consumers, and helps less tech-savvy users trust Apple's App Store.
Android has freer permissions on installing apps, because that is necessary for vendor adoption. However, it is unclear if this is still ultimately a better decision for consumers on aggregate.