Here's some stuff about training for punching that I wrote in another thread.
I think a lot of it is genetics. The best example I can give you is a baseball pitcher. The hardest throwers aren't always the more muscular/strongest guys. They are normally tall but some guys with a slight built have a great fastball... Pedro Martinez was an example at 5'10" and a generous 175. Mitch Williams who three 99mph was 6'3" but 180lbs (180lbs on 6'3" is SKINNY),... in fact very few pitchers look like they lift heavy (Roger Clemens being an exception for example). In fact many baseball pitchers are asked NOT to train their upper body that hard/heavy.
I'll give you an opposite example, a friend of mine play minor league pro ball. Th guy is 6'4", 230 and lean. Power cleans in the 300, power snatch over 225, push press about 300 too. And he has great throwing mechanics (go some tryouts for the majors).... yet he throws about 89-90, maybe 91 if he pushes it. That is 5-8mph slower than what a lot of much weaker/smaller pitcher are throwing in the majors. And in baseball, 2mph is a BIG difference!
Why do I talk about pitchers? Because I think throwing a baseball is similar to throwing a punch. As such I think the hardest hitters or pitchers are born to be that way. You can increase pitching and hitting power somewhat, but not as much as other components of MMA. That's why you almost never see elite boxers who are not hard hitters, become hard hitters... it just doesn't happen.
"But what about comparing punching to throwing a shotput? Is it much more different because of the weight of the shotput?"
Weight is a HUGE difference. In shot put you are throwing a 16lbs implement, in baseball a 140 grams/5oz ball, this is a 50x difference!!! And when punching you aren't "throwing" any resistance.
The heavier implement makes it VERY relient on strength, which is why shot putters are super strong.
\And the technique is a lot different than a throw or a punch.\
From your questions can feel that you desperately want to improve punching power and you WANT to believe that an average puncher can become a knock-out artist. But sadly oit is likely not possible. Otherwise don't you think that the "skill" boxers lacking knockout power would have worked toward fxng that problem and at least one of them would have found a strength coach who could accomplish that?
Your best bet if you want to punch harder is to get better technique and gain overall strength. You can improve... but if you aren't "born to throw a 98mph fastball" no amount of training can get you there.
AND I WOULD SAY THE SAME THNG WITH PRETTY EVERY SPEED OF MOVEMENT ACTIVITY.
In track for example it is often said that champions are born, not made. It's not entirely true since even with the proper wiring you still need to train; but you aren't born with the right neurological wiring and muscle fiber composition no amount of training can turn you into an elite sprinter.
You CAN get faster but you will be limited in how fast you can become.
Same thing with jumping.
Of course regarding punching power, if you go from a total weakling to someone who is fairly strong you will punch harder. But that doesn't go on linearly and not forever either otherwise all the hardest punchers would be bodybuilders and powerlifters.