Right, it wasn't Epic's pipe dream, but somehow that's the idea that got popularized on HN and elsewhere. For example, just a few hours ago the comments on the thread about the Supreme Court's declining to hear the case [0] were mostly operating on the assumption that developers would now be able to offer a substantial discount for people selling off the App Store.
That only works if developers actually could save significant money by selling through alternate storefronts, which was never going to be possible because Apple was always going to pick something approximately market rate as their valuation for the payment processor portion of the fee.
[0] https://news.ycombinator.com/item?id=39014642
For example:
> It seems easy to kind of shrug at this, but this does seem quite significant because of many mobile apps are 'free to play.' Apple pocketing 30% of all of these transactions, and forcing users/devs to go through Apple, is a major part of its revenue. And all of those apps now have the option to direct users to alternative payment methods, where they can both charge users substantially less and make more profit doing so.