Selectively permitting Netflix to have an app on the app store that does nothing unless you have an account with them and allowing them to not use Apple's billing system is 100% selective enforcement of the rules "because its Netflix", while other companies Apple doesn't care about or maybe compete directly with Apple's services are not allowed to do the same. This is a flagrant anti-trust violation.
I don't think that being selective with your business partners is necessary illegal.
Do you have an example of which someone lost an antitrust case because of this?