Whether iOS is a legal monopoly does not depend on market share in a common descriptive market segment, but instead in whether it in fact has market (pricing) power; that is, an antitrust market is in effect defined by where substitution actually occurs with price changes, not on how media/analysts describe markets based on product characteristics.
Didn’t know this, though. It makes a lot of sense, in fact.
Maybe. Market / pricing power is not sinple to assess, and I'm not sure if device / OS side or the application distribution side is most relevant to the browser bundling decision. I'd say it' seems to me more likely that the Apple has pricing power in the App Store that in iOS devices (it doesn't sell iOS as such, so that's probably not the thing to look at), and either device or app store market power, if it exists, could be leveraged against competing browsers with the policies restricting them.)
The law you’re referring to is “using a monopoly in one area to gain an advantage in another.” Crucial word being: monopoly. iOS is not a monopoly in the mobile market. Windows had 300 000% of the market, iOS has around… 20% worldwide? Let’s be generous and double it to 40%: still a far cry from a monopoly.