for example, do you think that present or past fighters such as matthysse, naseem hamed, valero, maidana, etc could hit harder than say - a super middleweight or a light heavy fighter?
Having such lower weight fighters might be a stretch. I don't think it's possible to see light or feathers hitting harder than super middles. Welterweights maybe.
According to ryan coyne (20-0 cruiserweight), golovkin hits harder than some heavyweights whether its true or not I don't know. “I’ve sparred with heavyweights who can punch, including Mariusz Wach and Mike Perez, nobody has hit me as hard as Golovkin. His power is out of this world.” Ryan Coyne, 20-0 cruiserweight.
Hamed could apparently punch as hard as a middleweight, im pretty sure Hearns at WW could put a lot of higher weight fighters to shame as well with his power
It depends on the level of fighter. A hard punching top of the line welterweight could probably crack harder than an average, nothing special supermiddle. From what I've seen and noticed, the top of the line guys (solid top 10 contenders and champs) overall seem to punch noticeably harder than the guys who aren't in the top 15 or 20. Not to say the others don't punch hard, but there seem to be some differences in power between levels of fighter too.
I think there is some truth in that, I am convinced that Tommy Hearns had the power of a middleweight at Welter, or even a supermiddle. When he hit people with that right hand they went to pieces. I also think that part of the reason why smaller guys are able to go up in weight and knock people out is there speed. The punch that fighters don't see tends to shock and hurt them.
Pretty sure Donaire hits harder than Malignaggi. In the amateurs I know a lot of LW's who hit harder than MW's with similar experience, but maybe the gap between fighters in amateurs is a lot bigger than in pro's.
There's also the difference in the type of puncher they are to consider; maybe Duran didn't hit as heavy as a middleweight Hopkins, but potentially hit harder (pushing SRL's teeth back, etc.) Probably not the best example but you get my point.
Here's a couple I think can hurt (and hit harder than some) heavier fighters: - Gamhoea (hoe for ducking Rios but I think he's got power to hurt at higher weight classes) - Pacquiao (I think Pac can go up another division and still catch some bodies) - Keith Thurman (supposedly he's knocked down heavyweights during sparring)