While I HATE Epic Games with a burning passion for brainwashing people and being very hypocritical, I think alternative payments should be a option if it’s not a developer trying to scam a user. Good, just don’t do Sideloading on iOS and I’ll be completely fine with whatever happens from here on out.
This is less directed at you individually (i.e. not attacking you) and more directed and responding in general to the spirit of your message ...
Regardless of how payments are done (1st party, 3rd party, or an In-App purchase completed outside of the app), as the judge pointed out, and then others went and re-read the developer agreements, the developer still owes 30% of sales to end-users to Apple, full stop. Which, before anyone else jumps to say is unfair, anti-competitive, or monopolistic, etc, it's the same as Epic -- itself! -- mandates in it's own contracts. They have different numbers for the commission level, but the point is, the commission (the 30% part)
is not as a condition of Apple taking in the money themselves. So even if you could use a 3rd party payment processor -- you still owe Apple their 30% first, then, the payment processor (on the whole sale amount, again) who will collect their own cut for processing and collecting the users payment. Epic, like I said, doesn't provide this "out" for any developer either. In fact, it's even more unambiguous in their contract compared to Apple's.
Epic's Unreal Engine license agreement:
"When you generate revenue from a Product or Distribute it to end users, you must provide Epic with advance notification at unrealengine.com/release, as early as reasonably possible, including the name of the Product, the format of distribution, unique Product id (where applicable), and the distribution channel(s). [...] You agree to pay Epic a royalty equal to 5% of all worldwide gross revenue actually attributable to each Product, regardless of whether that revenue is received by you or any other person or legal entity, as follows: (etc... )
Or to put it another way.... On iOS, you're hassling yourself, your customers, and costing yourself (as a developer) extra fees and commission using a 3rd party processor for in-app purchases or initial app sales.
Now Epic could have attacked Apple on the 30% number itself.
But they didn't. Epic chose to argue against the imposition of any commission at all. That is they stated they chose to breach their contract and do what they did because it was their opinion that any commission charge of any amount was unconscionable. (Despite the fact that Epic itself wants a commission for games developed with their Unreal Engine and games / apps sold though their store).
So again, Epic's core arguments and core case were super flimsy weak. But, they did win on the anti-steering, the only portion that they really didn't screw up.