And for most apps and (digital) in-app sales sold, it is - or would be - 30%.
Would you clarify that? According to Apple, 90% of the developers are small developers, and thus only pay 15%.
The 30% commission keeps getting referenced but that's only for the largest developers, and from my POV it is not an unreasonable cut from developers making millions off of Apple's App Store.
Looking at the stats in Apple's press release, I suspect most small developers will stick with the App Store since 15% is likely to be highly competitive with any alternative store and most alternative stores will not have the reach of Apple's. It simply make sense to stick with the most lucrative market.
Ultimately, Apple will find a way to keep the revenue stream from the large developers flowing in a way that satisfies the EU; and a few may chose to leave the App Store. I doubt they will however, because that means losing direct access to Apple's user base; many of whom will stick with the App Store as their default store.
I just do not see the EU ultimately requiring Apple to allow access to the App Store or all aspects of its tech for free. Looking beyond Apple, that would be a bad precedent and ultimately impact companies far removed from Apple.