It depends on what you mean by heavy hands.
I think Carwin probably generate more PSI per punch than Hunt. But I think Hunt has more of that "Touch you go down factor".
Look at Carwin's KO's, most of them were either a series of unanswered strikes(Mir), or a lower level opponent(Wain, Wellish, Pendergast). His only clean, standing KO against a high level guy was Gonzaga.
Hunt on the other hand has just put down some guys with epic chins. Kongo and Nelson are two of the most durable guys in HW history. Struve doesn't have the best chin, but he's a pretty solid striker.
When I think "Heavy Hands" I just think of those guys that have a inexplicable knack for putting people down. I just think Hunt has more of those kind of KO's than Carwin.