Not really, they can just leave it up to the court's interpretation. "I know it when I see it" has been used in a court before. Just define it as a smartphone: No one is going to call a gaming console a smartphone, nor vice versa.
And applying a ruling to a specific industry isn't new either: see that Hollywood anti-trust case again. It was never applied to TV shows. Otherwise Netflix Exclusives wouldn't be a thing. Or any other "Only on Disney Channel/Cartoon Network/etc" show.
They want to have their app/game store everywhere, not just PC and smartphone.
Also, hasn’t “I know it when I see it” been criticized as a poor test since it was stated based on how arbitrary it is?
It’s been used in a court, but not too much effect; the popular source of that is a discussion of “hardcore pornography” in a concurrence to a Supreme Court decision in an obscenity case which was notable for having a majority on the ruling in the case, but no consensus by any more than two justices on either a rationale for the ruling, or (among the dissenters) on the reasons for rejecting the ruling.
If you were, however, to penalize Apple; you would need to come up with a legal differentiation between a smartphone and a game console, as well as why the game console business model is moral and legal, but the locked-in smartphone market should be immoral and illegal. Considering there's no such thing as a "general purpose computing device" in the law; you would also need to come up with a pretty good explanation why Nintendo, Sony, and Microsoft get to keep their exclusivity privileges but Apple loses theirs.
And that's a tricky nut to solve. Because you might say, "well, a smartphone can do way more than a game console." Well, that's only because the game console is so locked down - but a game console remains theoretically capable of anything a PC could do otherwise. If it wasn't for a lockout, you could install Windows on it and use it as a node in a supercomputer. Does that mean Apple would be legally fine if the smartphone was more locked down then? It's tricky.