That argument didn't work for Microsoft in the 90's (just install BSD or buy a mac if you don't like IE), I don't know why it should work for Apple who's gotten much bigger than 90's MS.
But what about the other way around; how does Apple ensure that third-parties can compete with their private entitlements?
Is it even realistic for an indie business to compete against any of Apple's provided services if they're forced to serve that business through the App Store? Apple's progressive pricing scheme seems to punish them for posing a threat to any first-party services.
Any software maker is free to sell on any non-Apple device without Apple saying a word.