After reading this post a few days ago, I was curious and went to training to test out the damage. Although you are correct about SHs and SSHs being able to 2 shot, this is at an incredibly close range and dependent on armor stat. At mid range, SHs and SSHs still required 4-5 shots which are the same amount of shots needed to kill from LBs and LBXs. The scenario that you are talking about would be super rare considering most players have super spicy shifty movement. Now if you factor in having 2-3 bullets each, the chances are even slimmer. If the person with 2 SSHs manage to frag someone from the corner with 2 shots, I believe that the likelihood of him fragging with the remaining 2 would be slim considering that he's also been compromised. After dumping the remaining 2, the person is then forced to reload both his guns.

IMO the trade off of having 11 and 12 dmg for less ammo is well balanced.