Actually, not quite: Here's a quote from the wiki:

The exact potency of Phantom Roll results can be reduced for the receiving players if they are of a level higher than the Corsair. (ie, a level 75 job would receive a smaller attack bonus from Chaos Roll from a level 14 Corsair than they would from a 75 Corsair with the same number result) However, the Corsair still receives full potency. (ie. A party of 75+ receiving Evoker's Roll from a level 50 Corsair will lose the effect 1 1/2 minutes before the Corsair will)

Source Link

EDIT: Oh, and a mage is a useful healer for abyssea exp alliances the moment they have both Haste and Cure4.