It depends on how the court decides to define the market. Is the market limited to Fortnite on Apple devices? All games on Apple devices? Fortnite on all devices? All video games everywhere? The laws and precedents provide some general guidance but there's no clear and simple procedure defined for deciding what constitutes the "market" in the context of a particular case. Don't presume to know what a court will decide. In particular the legal concept of a product doesn't work the way you describe.