Also if people move away from giving Apple any money for the App Store, I expect the annual fee to increase to make up for it, and might Apple make you pay more if you don't use Apple's gateway? I don't see the ruling as forcing Apple to lose money.
If I were Apple, I would have gone nuclear early on, and eliminated all % fees but made the annual fee per app of $X to each developer (whatever $ makes sense) and then you can collect money however you want. This would likely kill a lot of small app developers, but the big ones would not care. The ruling makes Epic a big winner, but everyone else loses in the long run, because Apple (and Google) will find a way to recover lost revenue.
Some people also want to have 1000 app stores allowed. Good luck with that one... imagine having to build an app store just for your app, or supporting 25 different app stores.