I was the second best shot putter at school. The best was a bit shorter and lighter than me. But then the best javelin thrower was much smaller than either of us. He had no more training than us but was just a good natural athlete. He was good at every sport. Something about his run up and overall movement, rather than raw strength and size. If we were doing a martial art no doubt he would have had more KO power relative to his weight class than us heavier chaps. What are the factors that go into KO power:
Height
Build
Reach
Weight
Hand Size
Foot Movement
Hand Speed
Accuracy
Distance Management
Quick Reactions
Reading and predicting opponent's Movement
Set Up (Feints, KO Shot hidden in Combos, Hand Traps, Baiting a Response, Unpredictability etc.)
(Unexpected) Angles
Confidence in Chin, ie. you're more willing to risk eating one to land one
Technique, building the strike correctly through your whole body from the feet up etc. Although not if you're Shane Carwin.
Of course some of it depends on quality of coaching but a lot of it is quite unquantifiable and comes down to overall athletic ability. Like heart, you have it or you don't.