Scientific method:
You have a theory -- that the force of a punch is directly tied to the physical strength (lifting strength) of an individual.
You expand on that theory - this is still in the beginning stages, though you did some in the thread.
You see how well your theory matches observed evidence/empirical data. This is where you run into problems. There is a wealth of data available on both the subject of lifting strength (look to olympic power lifters, for example) and punching force. Studies done on boxers, in particular, present evidence that is in direct conflict with your theory. Some of the strongest punchers in boxing studies are the lighter weight classes (the guys with less muscle and MUCH less lifting strength than the heavy weights). Not proportionally stronger, just stronger punchers -- they generated the most force. Your theory that lifting strength is tied to punching strength does not account for this and would appear to be disproven by the data at hand.
So you need to come up with a different theory.
When you look at punching strength and what constitutes a strong punch, you find some rather interesting things that help to explain why some of the most physically strong individuals don't have correspondingly strong punches. If you have decent muscle definition in your upper arms, make a tight fist while feeling your bicep. Notice that it's tensing up? Now feel your bicep while you throw a punch -- notice still more tensing? That's a problem. Your bicep is responsible for bending your arm in -- that's the opposite direction that you want to go when throwing a punch. So you're actively fighting yourself in throwing your punch. Learning to throw a good punch is more about learning to relax all but the muscles involved in the act of punching itself (and there are a lot of them). Easier said than done....particularly in that you need to re-evaluate the motion of a punch in order to accomplish this -- your body has some pretty hard-wired controls in place to keep you from hyper-extending your elbow.
Those power lifters you thought should have good punching strength? They have pretty massive musculature -- it's a lot to get moving quickly (another part of a good punch) and it's a LOT to have fighting their basic punching motion.
And none of this even starts to get into transference of force, which is a whole other subject in and of itself...