White Mage is far from mandatory. My current play through is my ONLY play through to use a White Mage, and I'm actually finding it harder this time around.
The easiest team I've EVER used is a Knight Knight Knight Red Wizard. Your three Knights are going to be huge tanks, strong attackers, and light buffers/healers. The Red Wizard will play backup buffer/healer and throw in those nifty elemental spells and so on.
This team is almost cheating it makes the game so easy.
Now I've heard that a FULL Monk/Master team can be devastating. I know a bare naked Monk can be the hardest hitter in the game, but they also take damage extremely badly, and with no spells I just cant see how somebody would play this team.