From the first part of your comment, it directly follows that neither Apple nor Google has a required monopoly on the important medium.

IMO, we need to stop thinking in this broken paradigm of "-opolies" (with its loaded requirement to define what constitutes a given "market") and look at the actual coercive power they wield through market stickiness. Apple and Google both wield much coercive power with regards to software running on mobile devices.