I agree - Apple needs the control to have the leverage that makes their ecosystem better. It's in the interest of their customers for them to have this leverage and it requires that their 'store' is the only available store so app devs can't bypass their requirements.
I like Apple forcing use of in-app-payments, I like Apple giving me subscription control to make canceling easy. I like Apple blocking app tracking and forcing design constraints.
That said, the 30% weakens their entire argument about this and is a racket. If they want to charge a yearly deployment fee or something fine, but 30% of a company's income via IAP? That's obnoxious and anti-competitive, particularly in cases like Spotify where they directly compete and undercut them in the same market.
Apple is skimming a tax off the top and they're forcing everyone to pay the toll. It weakens their entire argument. I wish they would stop, because I think a world with multiple stores and such would be a huge pain and customers would suffer because of it.
If you think it's a pain to have 15 streaming services or 10 different game distributors all with their own shitty incentives - it'd be that on the phone.