Still, there's a giant difference - Amazon's "customer pool" isn't forced to buy only on Amazon and Amazon doesn't force YOU to ONLY sell the same item to that "customer pool" (I like how you use a term that makes people seem like inanimate objects.) via Amazon.
This is a massive difference. All the benefits of free market (as opposed to command economy) are derived from customers being able to freely choose another vendor and product to purchase. Monopolized integrated services are just a corporate version of command economy where a single actor dictates pricing and eliminates competition leading to severe lack of innovation and worse products for everyone.
At this point the 30% is basically free money they get on someone elses hard work. And there is no consistency, some companies pay much less.
This is even more wrong in case of Spotify which is a direct competitor to apple music. Apple basically makes their competition 30% more expensive hence less competitive. (And you can by no means claim Spotify is big because of app store so the fee is fair, they exited before the first iPhone)
what would be apple alternatives that would not imply giving away services for free? i still have an hard time understanding this part: i understand that 30% cut i a lot i am not defending the 30% tax.