I think the Black Mage is not on the Quick Poll because in FF1, he was limited to using a certain amount of spells each day from various levels of power, so he could conceivably destroy 9 villains and then be killed by a monster who usually would possess minimal threat. His ultimate spell was also strangely largely ineffective against the final boss, when it was most needed.

Orko is not on the Quick Poll because he sucks. His magic consisted mainly of making balloons, sparkles, floating, and in general, being worthless.