As far as the "Wraith outnumber Ancient" theory goes, I think it does makes sense. It's kinda like Russians vs. Germans in WWII, Germans have better tanks but Russians have more.
Or if you were to take an example from Stargate the movie, recall the two Jaffa that got swamped by the miners near the end... Sure they've got staff weapons but there were so many miners.
And here's a brief summary.
Starting the episode is McKay telling Weir that he believes the Ancient Orbital weapon can be used to destroy the hive ships. Weir agrees and McKay sets off with Grodin and a pilot (forgot his name). Meanwhile, John, Teyla, and com. are looking for another possible alpha site. Things go wrong and Bates accuses Teyla of unwillingly giving away information. John comes to Teyla's aid by explaining they ran into a T-Rex like creature. Teyla however, got into a confrontation with Bates but John stops her in time.
McKay and com. arrives at the weapon platform and managed to get the station on line. Grodin activates the AG field and McKay falls on the floor rather hard. A string of bad luck then ensued as McKay draws the short straw (pencil) and has to go EVA to fix the satalite.
Back on Atlantis, Bates is found unconscious from serious injury. Teyla is suspected and questioned by John. She is soon cleared by Beckett as he finds Wraith DNA on Bates. John, Teyla, and Aiden go after the Wraith in two teams. They managed to capture the Wraith.
Meanwhile McKay manages to get the station on line, just in time for the hive ships' arrival. The weapon fires and destroy its first target easily, however the weapon goes off line and Grodin is trapped inside as the remaining hive ships fire on the satalite.
After getting the bad news Weir declares the plan to evacuate the city. John get frustrated with their new prisoner and decides to kill it...