Why do Ninja and Monk use different gear?

[MiniPrinny]

To be completely straight forward, I'd have the following sets:

of Fending (Vitality/strength): As is, with one exception, the jewelry has half the STR of Slaying equipment.
of Healing (Mind): As is, accuracy is included as free stats on the jewelry in small amounts and on the chest and legs in larger amounts.
of Praying (Piety): An in-between suffix reserved for casters and healers who need to round out their MP reserves, used only on jewelry, this suffix comes with weaker scores for Mind and Intellect, but has both on it.
of Casting (Intellect): As is.
of Maiming (Strength): Heavier equipment used by soldier-type (dragoon, samurai?) melee combatants. Has higher defense than Slaying equipment.
of Dueling (Strength): Light equipment used by duelist-type (monk, ninja, red mage?) melee combatants. Has equal defense and magic defense.
of Ranging (Dexterity): Light equipment used by ranger-type (bard, machinist) ranged combatants. Has equal defense and magic defense.