You also have to dominate a market for antitrust law to even be applicable. Apple has less than 50% of the phone market in the US, which isn't enough to consider 'smartphones' as the relevant market in this case. They will have to argue the relevant market is 'apps for a single company's phone'. I'm not aware of any case that has successfully made an antitrust argument like that.
If that line of reasoning worked, conceivably this could open up a local movie theatre to being sued because they don't let you bring in outside food, or a restaurant with a great patio but shitty food sued by people who want to order a pizza from someone else to be delivered to their table in that restaurant's patio. Maybe some people think those things should be allowed, but the business world would fight tooth and nail against such an outcome.
The law generally treats "standing to sue" cases with a pretty low bar, so it isn't surprising that this lawsuit was allowed to go forward. I am surprised at how thin the margin was, and that Kavanaugh was the swing vote. He's already ended up on the 'liberal' side of a decision more often than I'll bet his supporters were expecting when they were loudly cheering his appointment.