When you use Apple tools to to make and publish software, Apple is entitled to a cut. The limitations Apple imposes on the payment processors are simply to make it easy to collect their cut and streamline the user experience.
I think the only scenario where Apple is not entitled to a cut is when you use non-Apple toolchain to develop your apps and spread it through non-Apple distribution channels, i.e. Cydia. Currently that requires a jailbroken device but maybe if Apple is forced to allow side loading, the cut for distribution can be collected by other companies instead of Apple.
[0] https://9to5mac.com/2021/09/14/apple-can-still-charge-its-ap...
“Apple has the legal right to do business with anyone they want,” said Paul Gallant, managing director at Cowen & Co. “So Apple could change the terms of the App Store and say to developers, regardless of where you collect your revenue, you owe us 30%, and if developers refuse to pay it, Apple would be free to de-platform them.”