For a guy to punch really well he needs to turn his weight ahead of his hands. Watch any good puncher and you'll see this. If your weight is behind your hands you are pushing your punches.
You can push pretty hard and guys have been successful doing it that way. But it leads to balance issues and defensive liabilities. When you do it right all the movements are the same and it all flows together.
If you are having a problem getting somebody to move the weight on their feet first have them punch moving backwards. Straight right, hook, uppercuts. You'll be surprised.