Even if they lose, they win. "Oh you can't play Fortnite on IPhones" is a seriously bad place for Apple to be. Don't even get me started on "Oh you can't use the most popular game engine to make games for IPhone". It'll shift market share toward Android, where presumably some users will learn to sideload and save Epic some money.
More likely it will shift market share to consoles. Epic will still lose their 30% cut and Apple will still sell what they did before. I do not foresee “can play Epic Games” as a phone marketing strategy.
I find it interesting that we still call those “phones” when for a sizeable part of the population they are mostly portable gaming machine to kill time when they’re bored.