That’s not what antitrust is about. Functionally speaking, you would not be able to prove there’s economic harm. Apple’s share of smartphone does not even compare to MSFT’s share of PC back in 90/00s.
This suit seems to follow the interpretation of: "it is bad if consumers are being harmed in some way". Having a monopoly position via market share is not a necessary condition for that to happen.
The Americans all say that to get in, you need an iPhone. So definitely a smart monopolistic strategy from Apple.
People excluding people is the problem. Not the product.