It feels like monopoly would be easier to prove: "There is no other competitor to provide an app on these devices and people depend on them for critical tasks". In a way, this mimics the breakup of Ma Bell. AT&T controlled all the phone service, and they also created all the hardware that ran all the phone service. Rather than divest their ownership of the hardware, AT&T proposed to break itself up, so "local operating companies" would own the last mile, supposedly creating competition.

Google could do the same thing by allowing device manufacturers (or whomever) to install their own Play Store, and users of devices could choose what Play Store to use.