Heres my line of thought,
Lots of people dont like having to free the cof gate in order to get into the dungeon. Why not make an server where everyone who wants to run cof can guest to? Since people can all pile on the same server due to guesting, the more people that are on the same map trying to get through the same gate, the less likely the bridge defence event will fail since there will always be someone outside at any given time.