While a level 6 Beseiged is planned and sounds like a 2-3 hour mess.. the following may help my PLD get XP for a change
and maybe I can go along and get in on retrieving the Astral Candescence ^^.

Experience Point/Imperial Standing Changes
- Rewards for Participation
The amount of experience points and Imperial Standing players receive for taking part in Besieged will increase, and a bonus will be given to all participants at the end of Besieged for defeating the notorious monsters that lead an enemy force.
The higher the level of the enemy forces, the more experience points and Imperial Standing players will receive.
- Retaking the Astral Candescence
The battlefield to retrieve the Astral Candescence became more difficult after the rate at which archaic mirrors appear increased. To encourage more players to tackle the battle, experience will no longer be lost in the event of KO in the battlefield to retake the Empire's greatest treasure.