The definition of anti trust is to use your position in one market to gain an unfair advantage in an other market. By denying Epic access in the game engine market, Apple is trying to get Epic to fold in the game distribution market. Thats text book antitrust behavior.
It is shocking to me that Apples lawyers, would allow Apple to so blatantly threaten Epic in this way. They are providing a clear example of anti competitive behavior, for Epic to use in future litigation. You would think Apple has good enough lawyers to put a stop to this self defeating behavior.