This one might be a bit loaded, but if Margarito didn't mysteriously lose his power after Cotto I, I think he would have had a solid chance in the rematch.
That's my take too. After all a far more diminished version of Arguello, fighting with nothing left but his power had a one shot stoppage of Billy Costello, a natural, much younger world class Jr. Welterweight ( Granted I know Costello didn't have the greatest chin, but still an impressive achievement by that version of Arguello) Some think all the knock downs Pryor had prior to the pArguello fights were a indication of a weak chin ( I thought that too) But after the Arguello fights and rewatching Pryor's bouts before, I came to realize it was more an issue of his reckless aggression than a chin problem. Pryor had a much better chin, and defense than given credit for. And skill level TBH.
Was that more an indication of Quarry''s chin , defensive acumen ( I.E ability to ride a punch) and toughness or Shavers lack of power? I believe it was all about Quarry's abilities.
Howard Davis Jr. One of the most talented boxers in history, and one of the fastest. Yet his lack of even average power cost him mutiple times in many of his biggest fights. Davis Jr. Maybe the poster child for this subject..
To punch with more power a fighter has to be willing to commit on his punches, if most fighters who are not known for power commit on the punch, it changes the way they fight. Instead of throwing lighter punches and trying to avoid what is coming back, they would have to shift their weight and follow through with their punches leaving them more open to the opponent's punches. A guy like Chris Byrd could probably have much more power if he set down and committed on his punches but he'd probably get hit hard a lot more often and it would change his "style." He'd get hit by punches that he didn't see coming if he was concentrating on throwing hard punches of his own. There is a reason that big punchers like Earnie Shavers are usually not known for their durability. ES may have been durable, but he committed on his punches and sometimes while he was concentrating on his offense he got hit hard by punches he didn't see coming. A fighter probably can't add power without changing the way he fights. If a fighter lost a close fight because of a lack of power, it might change the whole fight if the fighter fought in a way that he'd have more power.
A lot of the replies to this thread seem to more correctly answer the question, 'What if X fighter was a bigger puncher'? Because, for example, if Calzaghe was a bigger puncher, then his opponent(s) would doubtless have approached him differently, rather than going into a bout knowing they would take a few. To correctly answer the question of the OP, then I might say something like, if Mosely had the power of Jackson (when Mayweather took a freak rare punch to the jaw), then would Mayweather have been knocked out? But even then, if Mayweather KNEW that he was going in with a monstrous puncher, would he have even been hit, or would he have been more cautious!? It's a difficult question to answer!
Alberto Davila definitely fits the bill. Had great skills but his small size and lack of power held him back from beating the very best fighters.