Yes obviously. We'd need a mixed nash equilibrium (also known as rock paper scissor) around body weight :
heavy > medium > light > heavy
This is achieved by changing the prices of a set of weapon (say mg). So they fit best on light body. And then balance their damage with the heavy body armor level. This would make 1/3 of the heavy body armor useless against light weapons.
I don t think hardcoding the weapons so they can't be mounted on some bodies is a good idea, but improving the diversity around body weight would be great.