Summoning beats Black Magic any day (unfortunately for the Black Mage and the Magus/Warlock). A summoner is always worth using, both in the DS as NES version. Especially when you have Odin, Leviathan and Bahamut. I'm using one in my current NES playthrough (I refuse to use Ninja and Sage this time) and he's a powerhouse with Bahamut and Leviathan at his fingertips. ^^