Put it this way, do you think Naseem Hamed had massive hands? How about Tyson Fury compared to David Haye's?
It's a factor for sure but not the only one. Oscar DLH, Miguel Cotto, David tua, Tommy Morrison for example all had average or small hands
I feel big hands does increase punching power to a degree, but it’s just one of many factors. Imagine somebody who has exceptionally large hands, wide shoulders, tall, perfect technique and fast hands. Now this person is also fast muscle twitch dominant (explosive) and heavily muscled, particularly in the upper body. Now he may have stamina issues, but I do NOT want to get hit by that guy.
Smaller hands cover a smaller surface area. so theoretically a harder punch, as to bigger hands where power is spread out over a bigger surface area. Then power punching with smaller hands may break easier. So many variables. Its best to wrap your hands could and work on technique and accuracy.
Something that I never considered... The drag coefficient of a fist sailing through the air must be higher w/ bigger heavier hands. Hand size may be directly related to hand speed as well.
Tony Bellew has small hands for his height/size and has always been a good puncher. Its a bit of a myth me thinks.