I think the reason thief is good is because you can flee more often and you can use black magic like temper and haste which are helpful. I know that Blackbelts deals more damage overall but the fleeing power is just way too good.

Fighter
Thief
Red Mage
White Mage

vs

Fighter
Blackbelts
Red Mage
White Mage

Which do you think is better or do you think there is a better one?