Currently this is the case. Apple Music is held to a different set of rules and standards than Spotify.
When Apple Music wants to collect their customer's money from within the Apple Music app, they can do this practically for free - they don't need to forfit 30% of their revenue of that sale to another party.
When Spotify wants to collect their customer's money from within the Spotify app, they cannot without having to forfit 30% of their revenue.
Apple Music gets to play by different rules and is not held to the same standard as everyone alse on the App Store.
It’s hypocritical that they get to benefit from the more* level playing field in the Play Store yet force others on their platform to a restrictive policy, but it doesn’t seem contradictory. They are following the Play Store policy and are asking developers in the App Store to follow their policy.
The real question is whether or not their policy is legal.
Apple's Apple Music app is using a tactic on the Google App Store, while Apple's iOS App Store is blocking certain third parties from doing the same.
The implication isn't "Apple Music should be barred" but rather "If Apple is working around the 30% cut in other companies' walled gardens, maybe they shouldn't be blocking apps that try to do the same to Apple's 30% cut in Apple's iOS store"
This is showing up today because of Hey's rejection (https://twitter.com/dhh/status/1272968382329942017 more context)
The seller of Apple Music on the google play store is Apple Inc https://play.google.com/store/apps/details?id=com.apple.andr...
The developer of the iOS app store is also Apple Inc: https://www.apple.com/ios/app-store/ (check the copyright at the bottom)
Apple Music is in the same position as say Spotify on Google's platform as a third party media service. Is the implication that they should operate differently or be held to a different standard than Spotify?
I don't believe Apple has argued that collecting alternate payments in-app would be an undesirable for third party developers on the App Store - just that they don't wish to support it (for multiple reasons).
This also comes from Apple and Google having different starting points in their mobile platform - Apple already had a huge account and micropayment billing base for the iPhone by basing the App Store on the iTunes Store.