hehe 1 reason is the aoe. Say you have an aoe gun that has 20 dps. You also have a gun thats not aoe and has 25 dps. Casting gravity well, pulling 3 enemies, with the gun thats not aoe, you deal 25 dps. about 3 seconds for 1 kill. Now, if you use the aoe cannon thingy....after beckoning, you hit ALL enemies. 3 seconds for 3 kills!!!

^that^ is just a simple thing...YOu might wanna do some tests though. And question! Is the level 20 green commando gun aoe? Im pretty sure it is (checked today) It seemed to gather mora aggro than my other gun. because im hitting every enemy.

Thats just what I think....