At lot of punching power shifts through the twisting of the hips. How the hell does a squat replicate that?
Take the blinkers off dude. Not everything in the gym is going to be directly applicable, but that doesn't mean doing it different won't provide a benefit.
if you throw an upper cut correctly you come up from a bent knee position to full extension ie. you do a quarter squat, similar to jumping
but you don't squat down into the full squat position to throw a punch
in fact there was a study done that showed that quarter squats were superior for improving jumping ability and 40 yd dash speed as compared to full or half squats
and ok, I lied as I do more of a quarter squat than a full squat but if you get really fucking technical about it its probably a 1/3 squat