The fact that Apple has made itself the only market available is what makes it anti-competitive. Even then you could argue that's what you bought on to when you opted into their currated ecosystem.
Apple and Google's customer reach is a direct result of them footing the effort to create a store and relationship with OEMs and currating the store in a way that works for the customers that use it.
If Google hadn't tightened the rope on the Play Store polices, it'd be a mess, just like it used to be and like some 3rd party stores are, not user friendly and full of low quality or malicious apps.
This doesn't change the core of the argument. Companies and customers have their free will. If a company doesn't serve quality products in their store, customers will leave, if they make their store too painful for other companies to host in, so will they. If you agree to a contract and don't follow that contract and get booted, that's in your.
If you want reach into Apple's customers, you have to buy in to the whole deal, doesn't make them right for being the only store for their ecosystem, but doesn't make you right for giving them the bird and crying foul when you violate the policies agreed upon.
I won't buy the argument for Android you're throwing out there. Publish to another store of you don't like the Play Store, I do. Google's store is their customers, and their customers to make policies to protect from bad apps. If another store was better, people would use it readily, and they have the open option to. That's why FDroid exists, don't like closed software, well it doesn't exist there, and the customer made that wants it uses it.
Bottom line, you sign a contract and agree to the policies, don't cry foul when you get bit for violating it, like anything else. You put yourself and your company at risk by not reading and understanding what you agreed to.