If you have three guys armed with two AK-47s and one pistol the two guys with rifles can sure as heck drive their opponent into the field of fire of the guy with the pistol a lot easier than three guys with one pistol.
The fact remains that two "gunwalker" guns were retrieved at the site where Agent Terry was murdered. 1,400 more "gunwalker" guns are still walking around Mexico. Or back into AZ like those two.