A monopoly can be so many things that the question needs to be "is it causing harm?"
For example, a trademark or a copyright or a patent is a monopoly on the use of that IP, and those are considered "good" by the governments and courts.
In my (IANAL) opinion, I think the important question for a mobile app store needs to be: do users and developers have a meaningful choice between iOS, Android, and just a website?
I really don't know the answer to that, though I expect the market share plays a part in it — if iOS was 10% or 90%, then developers surely would not have any meaningful choice.
For example, a trademark or a copyright or a patent is a monopoly on the use of that IP, and those are considered "good" by the governments and courts.
In my (IANAL) opinion, I think the important question for a mobile app store needs to be: do users and developers have a meaningful choice between iOS, Android, and just a website?
I really don't know the answer to that, though I expect the market share plays a part in it — if iOS was 10% or 90%, then developers surely would not have any meaningful choice.