The Apple/antitrust angle has been covered, but this Direct payment bypass also affects Microsoft, Sony, Nintendo, and Google. Won't they take issue with it as well?
Apparently the cuts that Microsoft, Sony, and Nintendo take are already acceptable to Epic. The announcement says that those users are getting the discount automatically without taking any action.
Starting today, any V-Bucks or real-money offers you purchase on PlayStation 4, Xbox One, Nintendo Switch, PC, and Mac are now discounted by up to 20%. You don’t need to do anything!
> If Apple or Google lower their fees on payments in the future, Epic will pass along the savings to you.
and
> Do you play Fortnite on Android, but don’t purchase through Google Play? No problem! You’ll find that V-Bucks and real-money offers are now discounted by up to 20% through the Epic Games app at epicgames.com and the Samsung Galaxy Store.
Both of which strongly hint to the idea that its specifically the rates the Play/App Store charge at issue here, and they likely received discounted rates on competing storefronts by default.