Yep, the ruling seems to cover exactly that plus stopping Apple themselves treating in-app purchases and subscriptions (from actual App store apps) differently to how they currently approach physical goods (which are already allowed by Apple to go via other payment channels without any fee, or a developer might choose to go via ApplePay with possibly slightly less effort).

I agree, the end effect should be them charging say "5% of something" and the developer choosing not to bother thinking about external payments. They seem to avoiding this outcome on purpose though. (I dare say Apple might prefer to chase advertising revenue from the app store rather than accept small fees, but they'd risk trashing their own garden).

You can't argue that 30% is reasonable when your competitors want to offer that same service for 3% (transaction fees).