Eh, while I’m staunchly against Apple's integrations, the App Store isn’t a relevant factor imo.
These are things inside one store, as in Spotify and Apple Music are both for sale in the one store, and while Apple takes a cut, which could force Spotify to increase their price, they do have full pricing autonomy.
I’m not entirely against the fact that Apple has a walled garden in the form of the App Store, just because they do seem to invest in keeping a certain standard of quality unlike Google, but I’d say that’s a separate issue.
And Spotify probably doesn’t want to be in the store business anyways even if Apple allowed it, Epic Games is probably the first major case I heard of a company doing similar on Android (where it’s allowed) and almost immediately they opened a security vulnerability into everyone’s phones so...