I'm picking on Netflix but the point stands - many companies are able to stand up payment processes. It's not a hard problem and it's not uncommon for companies to have them.
"because apple" isn't a reason to tax a company 30% for things like Netflix that are only tangentally iPhone or when a company can provide a standard level of payment processing.
Apples payment processing isnt THAT good. Definitely not 30% good.
It is not ok to block any other option or even mentions of external options when you are also the gatekeeper of the only marketplace.
The monopoly Apple has in this case is on distribution of software to iOS devices. They are leveraging this monopoly power to maintain a monopoly on payments.
Antitrust laws say this leveraging should not be allowed.