Indeed, there has to be per the "case or controversy" clause of the constitution. For a plaintiff to meet standing, there must be an "injury in fact".
Epic must violate Apple's terms of use in order to be injured by the application of them, in order for Epic to have standing to allege those terms are an abuse of monopoly power.
That is incorrect, the 30% that Epic was paying Apple was sufficient to establish standing, they did not need to break the contract on top of that. The judge said so herself during the trial.
Fun related fact. Cases where a law is violated specifically to seek a precedent on appeal is sometimes called a test case. Tons of famous civil rights litigation were test cases where one or both of the parties purposefully sought an unfavorable verdict in order to appeal. Plessy v. Ferguson, the Scopes Trial, and Brown vs. Board of Education were all test cases.
IIRC the legal community used to kind of dislike these, and I think there might have been a penalty for doing it. But obviously that’s no more
Epic must violate Apple's terms of use in order to be injured by the application of them, in order for Epic to have standing to allege those terms are an abuse of monopoly power.