Earlier quoted context omitted.
Did you read the link you just posted? Seriously. It clearly states what I said, and contradicts what you said. As per YOUR LINK, you don't need a monopoly for antitrust; just "the ability to raise prices above those that would be charged in a competitive market." Apple unambiguously has this with their app store.
Not all antitrust violations require monopoly power, that is true. For example, price fixing is illegal even if the companies involved do not have monopoly power. However, several of the claims Epic made in their lawsuit do require proving that Apple has monopoly power, which is going to be a difficult argument with their current 46% market share.
In either case, the standard legal approach is to throw the kitchen sink of claims, to see which ones stick. Most claims get rejected by the courts, but if you have a few that work, it's enough.
It also helps settle. If I have a dozen $10 million dollar claims, with a 5% chance of success each, a rational opponent will throw me $6 million to go away. If the parties settle, the kitchen sink approach is not a bad one to get a better settlement.