The only problem here is that you have to show Apple changes practices to become anti-competitive once achieving large marketshare/control.
It's OK to have a monopoly, it's not ok to abuse it under U.S. law.
Apple has actually loosened restrictions over time as the platform gained marketshare/size. And when Apple created the App Store they more than doubled how much developers took home from gross revenue (70-80% of revenue went to distributors/retail prior to the App Store).
The only anti-competitive area I'm concerned about is Spotify/streaming services. I think Apple is being overzealous here.
Everything else appears to be a game/software distribution norm.
Epic pays 30% on Android, Nintendo, Xbox, and Playstation markets.
Steam needs 15% and GOG needs 22% of gross revenue from games to break even operationally.
Stripe charges about 3% of gross revenue for transaction services.
The 30% doesn't seem that high when you consider those factors:
15% just to keep the lights on (Steam break-even royalty rate).
3% for transactions at minimum (e.g. Stripe fee)
Ongoing R&D costs of maintaining iOS/iPhones (more technically and cost intensive than Xbox and Playstation combined).
The kit for iOS development is remarkably cheap too, $99/yr developer account (mostly a gatekeeping path to keep malware out), and $700 for an M1 Mac Mini (If you don't want to just use a VM from AWS for < $100 yr).
I think they can do better for small-time app developers (the 15% fee has helped), but I still feel like these people should STFU and look up how expensive Gaming Console, Embedded SoC, and IoT dev kits are in comparison (And god, don't look at the agreements we sign on embedded hardware dev kits). I wish I only had to spend $99 a year, and be able to use $100 used cell phones to test my software on.