I linked to Epic v. Apple, where that exact argument was made and the court sided with Apple. It wasn't a DOJ antitrust suit, so maybe the rules are different t

I linked to Epic v. Apple, where that exact argument was made and the court sided with Apple. It wasn't a DOJ antitrust suit, so maybe the rules are different there, but in that case Epic tried to make the argument that the relevant market was iOS app distribution and Apple therefore had a monopoly. The court ruled that in order to make that case, Epic had to demonstrate (among three other tests) that "the challenged aftermarket restrictions are “not generally known” when consumers make their foremarket purchase". The court found that consumers do know about the restrictions in advance of making their initial purchase decision and therefore found that the relevant market had to include more than just iPhones.