Any fighters that you can think of that started out as a light puncher but later on became a harder hitter? The first guy that comes to mind would be Sergio Martinez. He didn't have much KOs earlier in his career, but as he progressed he seemed to have better punching power.
I wouldn't say they didn't have it but for whatever reason, developed the technique or mentality to get the knockouts. Martinez definitely. And he carries it late too. That matters. As his opponent is more vulnerable, he can still be explosive. Hasegawa seems to have turned something on later in his bantamweight career. He had a very low kayo ratio, and he started to obliterate his opponents, and early. Before Montiel, his five opponents in all world title matches, nobody got to the second half with him. He seemed one dangerous SOB there. Still has a 38% kayo ratio. Strange, the way that worked out for him.
Martinez is the obvious one. I'm not sure Saad Muhammad/Franklin would qualify since his power increase came in his prime, and his increase came with a complete style reversal, but still he was one of the best punchers ever at 175. I think he had legit one punch power, but his opponents were often so tough he had to land a lot of 'one punchs'. Just a thought. Carlos Palomino insists that his punching power radically increased with the confidence he gained from winning the title. I'll take his word for it.
Marquez and Hearns (post amateur) are usual shouts in these kind of threads. I'm not familiar enough with both of their early careers to be sure, to be honest.
Pernell Whitaker shows glimpses of decent power late on in his career. I remember him salvaging the De La Hoya fight with the somewhat desperate stoppage of Hurtado.
Hozumi was balance related. And a lot of Jap' fighters have low K.O ratios when they start out but turn it on for the important fights, Shozo Saijo being a notable example but Sakurai dropped Rose and Tanabe battered Accavallo.
He was always spiteful but as his legs left him he had to sit down on his shots more. Never topped the Nazario K.O for me. Pretty durable opponent by all accounts.
I thought about Saad but you've already touched on the reasons why; -Matched ridiciulously tough early on -Totally changed his style post-Gregory -Fought in a great era of both durable tough guys and stylish evaders The Mwale K.O proves he's in the ATG category for 175lb punchers for sure. And Johnson's chin is painfully underrated, he could be stopped but it took a lot. So yeah, I'd say Saad was always a big puncher but thanks for making me discuss the thought I had when I saw this thread earlier :good