In my mind, if company produces a product (iphone) they have the right to do with it as they see fit. Don't want to allow apps from sources other than app store? Fine. Ban the app? Fine. Now, why is this fine to me, no one is forced to use the iphone or use the app store. Don't like how apple does things? Buy android. You and others (Epic, other ios developers) are complaining how apple does things but you want access to their users...
In summary, I personally don't like their policy as well, but no one put a gun to my head and said you have to buy it. Same in your case.