Okay, let's simplify.
Your arms are a certain length. Longer arms are both longer from shoulder to elbow, and elbow to wrist. Taller guys can't change that. You can only bend at the joints.
Imagine your arms as extensions of yourself similar to melee weapons like a baseball bat. You step up to the plate ready for a pitch. You situate yourself so that in your stance, without leaning, you can touch the tip of the bat to the opposite side of the plate. Pretty standard range-check. Except, now, imagine this isn't an open-air environment. There is a concrete wall perpendicular to you cutting halfway through the plate; running in a straight line from mound to the catcher. It's as if you're in a tight tunnel, with your back up against one wall, but a tunnel that is so narrow you can't swing the bat naturally extending your arms without the bat coming into contact with the opposite wall well before you have generated maximum power, and the bat crosses the plate.
You have to choke up to swing through, or the bat's arc is cutoff by the opposite wall. Except you can't choke up any more than you can unhinge your shoulder from its socket (without dislocating it and injuring yourself).
Now, do you want a full-length bat to swing in that tunnel? Or do you think a shorter, fatter, but equally heavy bat would be a better tool to generate power in that environment?
This is a timeless truth. It's why the ancient Japanese crafted short swords intended for the niche of fighting indoors. Outdoors, the longer katana has superior range, and is therefore preferable. Range always wins given space. That's why we evolved archery, artillery, firearms, and ultimately ICBMs. I hit you. You can't hit me. No exchange is more desirable.
But when a short guy has closed the distance, and gotten inside, you don't have that space. You are fighting in a choke point. This is true with straight punches, too. The shorter man is able to fully express the proper punching technique, and achieve maximum velocity on his punches within a short distance. He isn't expected to hit as hard when the taller man is able to express his full range, since the taller man has more distance to create velocity, but even given equal distance in that box, angular momentum doesn't favor the taller man's longer limbs, nor his wider stance/shoulders.
When I say "angular momentum" I'm referring to our bodies, and the nature of our muscular strength. Think about it. Are you concentrically stronger when your knees are fully bent at a 90-degree angle in a squat, halfway bent at a 45-degree angle, or for the final 10 degrees when you stand up? Lifters exhibit different weak points across a complete lift, but generally speaking, we are all much stronger in that final 10 degrees than we are in the first 10 degrees transitioning out of the hole. The same is true for the bench press, and for our punches.
Make sense?
