Not fully capable, I believe it lacks some buttons ? Like the second joystick. But, if the game is designed with this in mind, then the joycons are more than functional!
Yes, it's great for Mario Kart (before I got the Pro controller, my wife and I were playing with one Joycon each), and similar games (I assume ARMS and 1-2 Switch are built with single-Joycon use in mind) but it's not enough for every single game.
>The fact that a single controller breaks up into 2 fully capable controllers still surprises me to this day.
Right, each controller on their own is not fully capable. That said, I think it's an impractical goal (really; how would you play a game like BotW with one hand? Impossible.) and I'm not sure the Gparent meant it that way.
Looking back though, I either misunderstood the OP or the parent is correct. One joycon is obviously not fully function on its own, I never meant to say that.