The consumer welfare thing is just one factor of many to make a status-quo antitrust law case a real battle. There hasn't been antitrust victories for consumers in a very, very long time.
Epic had to get Apple to go do an anti-trust thing - in their opinion. So it's definitely required to bolster the claim.
Probably 100% of congress uses an iPhone. 100% of judges. Every lawyer. It's right in their face. 100% of them use Google, 0% use Bing. I don't think I know a single non-engineering professional, English as a first language adult who uses an Android device.
It's not some abstract situation the consumer welfare standard didn't anticipate; it's the now. Nobody is going to sympathize with arguments about choice because that hasn't been true for a while - nobody makes the choice, not among these people, for alternatives, so is there really a choice?
Looking at the Wikipedia page and the requirements for standing the way Epic is doing this looks at least for me much more in line with the given requirements.
Though I guess the Wikipedia page is a simplification of the reality.
I have a feeling their money on iOS is a rounding error compared to the serious gaming platforms, and this whole thing is basically a marketing activity that they calculated would pay off better than the revenues they'd lose from losing access to iOS/Mac.
Also considering if they win this much more clear cut case, then they or someone else would try to apply it to those markets.
The case is definitely clear cut, but not to Epic's advantage.
I have no love for Apple, but at the same time Epic doesn't have a leg to stand on here. This is two extremely wealthy parties fighting over a giant pile of money, and Epic is cynically trying to claim they're fighting for the consumer.
If the underlying structures wouldn't change it would be a smaller pile of cash more parties share. On the other hand, if it opens up for innovation the pile would grow allowing better products for all. Though I guess the innovation angle is hard to prove in court.
Wait until Epic gets their app store entrenched and raises their prices for Fortnite content 30% because they know people are willing to pay that already, and no matter how much they raise the price, it's always the cheapest option.