The real issue is that Apple has control over its devices after sale. That it decides what they can and cannot run based on its own arbitrary rules that no one can challenge. That it can literally put other companies out of business by denying them the privilege of having an iOS app.
"Apple controls 100% of the iOS software market. This antitrust case is not about phones, instead it's about iOS software, and we shall demonstrate very clearly how Apple are abusing their total monopoly on that particular product."
I've seen this comment repeatedly on this site. Presumably the posters making it don't actually believe we have a world government that rules over all countries, yet they keep making the assumption antitrust rulings happen over world market share.
The real issue is that Apple has control over its devices after sale. That it decides what they can and cannot run based on its own arbitrary rules that no one can challenge. That it can literally put other companies out of business by denying them the privilege of having an iOS app.