The size matters, Ali did hit harder than hearns h2h even when hearns was a killer puncher in his own division and Ali was not even a puncher at hw. It is the same that one idiot said once that Morrison had "welter chin", morrison would have iron chin facing light heavyweights
Maybe this is the answer. Aust 140 lb Steven Spark who is 9 - 0 and 9 ko vs stablemate 110 kg AM in street fight. Spark did some damage. This content is protected
This is a somewhat unfair question. JJ was able to bring his power to bear and set his feet against similar sized opponents. Byrd was nearly always the smaller one in his division so he could never adopt a hard punching style, since his mind was set on defence. Let Byrd set his feet and wing them in, and I think you'll be surprised at how hard a "light hitting" heavyweight can actually hit.
Thats different though. Big guy didnt even look like he wanted to fight (might not be fair to say when the other guy is literally walking away) and it looks more like he got overwhelmed by the speed rather than the power of his punches