While it may provide a comforting myth to believe that "market" is in some way inherently "smartphones as a whole", or "personal computers as a whole", and therefore by definition it is impossible for Apple to be a "monopolist" - that's really just the same logic that says "America waterboards prisoners, America doesn't torture, therefore Waterboarding isn't torture".
The more complex truth is that "market" as a definition has been developing in multiple cases, both in America, and internationally. Increasingly, it is being defined more narrowly, such that iOS itself is a market, within which Apple will face increasing scrutiny over their actions to prevent developers from using competitors to Apple's own offerings for App download hosting, and payment transaction processing.
It's ironic the more that Apple does to differentiate its own devices and platforms through unique integrations and features, the more they reinforce the impression that they are not merely players within a larger market, but constitute a market on their own.
Epic's entire case has revolved around the fact that Apple charges Epic 30% of their revenue, for a service (app download hosting, and payment processing) that Epic can provide themselves for ~1/10th of that price.
The fact that Epic also has their own app store for PC games, and could easily compete with Apple in providing an iOS-native appstore that independent developers could sell their apps through, yet is unable to, because Apple controls the iOS market in such a way as to exclude competitors, is exactly the sort of thing that antitrust legislators world-wide are currently examining.
Unlike the economies of games consoles, where console makers eat a loss on the device in order to cut the entry price for the consumer & provide the largest possible addressable market for games developers (which would justify a large cut / exclusive store position to make up for that loss), Apple makes a profit on the hardware and operating system at the cost of reducing the overall size of the addressable market for iOS developers.
As for Apple's previous conviction for antitrust violations, Apple had access to the best lawyers money could buy, and the full range of appeals in the US justice system, yet they were still convicted and sentenced, so maybe it's time for Apple fans to accept that it doesn't matter why Apple broke the law (because Amazon was a market abusing 800-pound gorilla), or who else was breaking the law, the fact is Apple DID break the law, which is why they were found guilty - Apple colluded with publishers for the purpose of raising the price of Ebooks. That's not some civil contract that two companies can disagree on in court, as per Apple Vs. Epic, that's committing a corporate felony against the citizens of America. Fundamental to any civilised system of justice, is that guilty parties are supposed to acknowledge their guilt, and reform their behaviour.
Twain remarked that if you give a man a reputation as an early riser, he can sleep in till noon without consequence. People need to stop considering Apple's actions in light of its reputation, and start reconsidering Apple's reputation in light of their actions. Apple is a convicted antitrust felon, and it is appropriate for courts to view any competition disagreement in which Apple is a participant, through that lens.