No rocking an opponent in a fight means they landed a good shot (either accuracy or power can do that.) Being good at it means you regularly knock people out and win fights that way (consistency.) Those are the fighters that we typically agree are heavy handed. Chris Leben is a guy who had heavy hands and was always a threat to KO. I don't consider Gilbert Burns to be a KO threat. It is not a common path to victory for him. Gilbert Burns is a decision threat, especially now because he's undersized for 170.
I don't agree with your comments on fighters above. Matt Hughes was *always* heavy handed and has a lot of KOs and TKOs on his record from day 1 (not all from punches though.) Matt Serra is pillow fisted and has almost no KOs. He got a lucky elbow once (seems like a lot of people see one case and development delusional bias.) Tito has a few KOs.