Why was the Dungeon of Dorukan so easy?

[Peelee]

In fact, Lirian's was the Gate with probably the weakest defenses. I mean, were it attacked by that version of Team Evil which assaulted the other Gates, her trump card (the anti-magic virus (and, for that matter, any kind of virus)) would have failed to so much as tip the scales: Xykon would have been unaffected, Redcloak would have been unaffected, and were they to bring along a few ghouls, ghasts, wights and perhaps a couple major league undead monstrosities (the decoys come to mind), the whole business would have been little more than an evening walk for Xykon &Co.

"Weak to one specific possibility" does not mean "weak overall." Heck, if we're going by that metric, Girard's Gate was the weakest, since the defenders were all dead and Xykon knew the exact location.