That's the thing: you can make someone sign all the ToS you want. But if those terms of service violate the law, it's all wet paper. Like, I can sign a contract that makes me work 15 hours a day, no days off and that make me pay for my own PPE. But since all of that is illegal (at least in my country) the contract means absolutely nothing.
So, what they have to do is see if Apple's ToS contain any abusive/illegal clauses. The fact that Epic signed a ToS is not an automatic win for Apple by any means.