Why was the Dungeon of Dorukan so easy?

[Tvtyrant]

True to an extent, but the nature of Lirian's Gate made it easy to keep Lirian away from the rift, making it extremely vulnerable to Redcloak just casually walking up to it.

Absolutely, it did not work. We know it didn't work. However it's the why that matters here; Lirian's defenses would have worked if not faced by an out of settingly strong Lich and an army they had not anticipated working together. Her forces were enough to guard the gate while she dealt with major threats or vice versa, except they faced two major threats at once including once.

Lirian was quite right that the largest threat was a high power caster so she built a macguffin for it, then got beaten because Xykon became a Lich (which no one else knows about but Redcloak), was a higher level character then anyone else in the setting, and had an army.

Edit: Static defenses are also not meant to win but to slow enemies. If Xykon had been met by all of the Scribbles this would not be a series, but he wasn't because they had made monumentally bad decisions. Again, none of them call to the others for assistance, even Dorukan doesn't pop in to help.