Actually, the Cloak of Mirroring does protect against hostile AoE damage spells. Father Wrathful died through a much simpler way. Something which a BG2 Cleric has no defence against, save Potions of Invisibility (which he/she will have to drink before the Time Stop starts).
The Cloak of Mirroring is powerful... but it does have its' weaknesses.
My comment about Abjuration was in response to statements of Clerics being able to buff up to the gills. It is one area where Clerics falther, while Mages excel. A very unbalancing equation, when you think about it.