NIN is the best Tank for a NON BLM Enemy since Shadows are wiped by "-AGA" spells it is a BIG BIG Weakness of us, Ninjas.
However NIN are also best Tanks 'cuz of our Evasion Bonus and Armor, Even tho it could be PAR with THF's but it is only 10 Less skill 2nd BEST EVA Job in GAME
NIN/DNC is nice to tank because it can "Violent Flourish" the "-AGA" the BLM Mobs do, not 100% Stun as any DNC can tell you, but it works.
for Holding Enmity, CAP Haste (26%) and Dual Wield (50~56%) and Weapon Skill Strong and True.
I hope this have helped some new Ninjas looking for GOOD Advice, Peace