Hmmm ok........fail to see how's that even remotely similar. iOS is well, as it name implies and Operating System, which provides a platform for third party developers. Fortnite is a piece of SW with a single purpose (otherwise known as a game).
It's similar in that just as Epic rightfully has complete control over their game, Apple has complete control over iOS. Years ago before smartphones there were no App stores and phones came with a set of default/basic apps and that's what you got. Apple could (theoretically, and legally...not practically) go back to just offering stock apps that they create and not allowing others to submit apps for iOS. Publishing an app for an operating system (iOS in this case) is not a right that developers have, Apple gets to set the rules (in this case their commission rate/payment methods allowed) and enforce them since it's their product .