Apple shrugs and bans Spotify. Next move?
Having a monopoly over their own product is what every company has.
I think the confusion here is that you incorrectly believe this is a necessary condition for Spotify's complaint to be upheld.
phone choices are inelastic. users do not drop phones and switch to a competing platform because they cannot install an app, it's the other way around. besides, with that logic you have no guarantee against ALL platforms becoming locked down (as they more or less have) to compete.
Well, it wasn't just an app, but that was a pretty big reason (though not the only one) for my dropping iOS.
Potential antitrust issues notwithstanding, it seems like such a message would be very much aligned with Apple's interests.