The poster you were quoting might have other, further qualifications for their comment, but here's how I'm looking at it:
Consider that per (my understanding of) the ruling developers will be allowed to offer non-Apple payment options.
Consider also that per (my understanding of) the ruling Apple is allowed to continue to charge developers fees for services that the 15/30% cut used to cover.
Consider a hypothetical where Apple splits that cut so that they charge 5% if you use Apple's IAP system for payment handling (but you can use other payment handling systems, such as Paddle's), but regardless you still need to pay 10/25% to cover everything else that Apple is charging you for.
Going 100% Apple systems you'd pay 15/30%
Going with Paddle for payment processing you'd pay 20/35% (10% to Paddle, 10/25% to Apple)
As said this is hypothetical of course, since we don't know how Apple will charge developers under this ruling, going forward. But it's an example of how things might go.