Yea but in the SG1 ep when they discover the earth defence station and O'Neil Fire the drones, they don't explode, they penetrate and carry on. One massive wave of them could chain attack the whole fleet. Plus Atlantis has docking stations that could carry several earth ships like odyssey and Daedalus which could be secondry defence also. And they could maintain life support in the central tower of Atlantis with the gate active for nearby escape if need be. (Massive stargate geek here) haha