The Traitor's End
It was like both sides were heading towards the end in different ways. The enemy focused its entire tactic on trying to breach the mine field while the allied forces of Amera, Nicole, and Doaf kept their best to eliminate the powerhouses of these enemies.
The mine field was the brilliant idea of Deem himself. He acted upon the old orders from Arthur to maintain the defenses of the sect intact.
In fact the presence of a traitor was something they knew of but didn't know who he or she was. And so they just assumed the worst and started to think of ways to sustain the sect.
Even if the shields were gone, they implemented a lot of other defensive tricks which the mine field was one of those.
In return things inside the sect seemed a bit chaotic.