This is a strange take considering Facebook is distributed for free in the App Store with the current model. Apps paying the 30% tax _already_ subsidize Facebook’s distribution.
Does FB have in app purchases on iOS? If so, is 30% going to Apple as the processor?
Facebook is completely ad-supported. I guess the hole in Apple's revenue model is that they don't charge 30% of ad sales (of course I think this demonstrates how absurd the whole idea of charging a % of subscription revenue is.)