I think lower tier (L) amps are fine, but as they get bigger their mark up increases by a lot, not to mention horrid decay and use of 3 or more additional ammo cells per shot, adding all of those factors and the mark up, they are just not very economical to use.
I think, if MA would let (L) amps to work as pre amp nerf amps, then their demand would rise, but as of now, they are just a more expensive version of the amps already in existence.