[tzs]

I don't see any way to even ask the question sensibly about iOS.

Google supplies an OS (Android) to non-Google phone makers, and Google supplies applications to non-Google phone makers. The potential antitrust issue is if Google is using its position as an OS supplier to other companies to influence those other companies to also choose Google for applications.

Apple supplies neither an OS nor applications to non-Apple phone makers. There is no third party that Apple is using iOS to influence toward choosing Apple applications.