iOS is not a market segment. Smartphones is the segment and so you do have a choice. The courts have already ruled that Apple doesn't have a monopoly in their segment.
That's not what the courts have been saying lately. iOS app distribution and Android app distribution have both been called relevant markets in recent trails.
I think you're conflating their designation as "markets" because they are marketplaces of apps with the economic term "markets" which has a specific definition for a sector of industry.
no conflation at all. read up on some of the trials for Google and Apple over the last couple years. The anti-trust trials aren't talking about a "super market", they're talking about a relevant market in anti-trust context.
You’re discussing this in the context of a case that deemed that it wasn’t an anti-trust violation because it was determined Apple doesn’t have a monopoly, though. They’re not considered their own markets.
The first half of your claim is false, "iOS app distribution" was not accepted as a valid "relevant market" in the very court case being discussed. But I think you knew that already.