I would like to suggest a modification to the NINJA (NIN) job that would help improve its usefulness and therefore demand as a tank.

Changing shadows so they are not instantly wiped by any/all area of effect (AOE) attacks, I believe, would be a step in the right direction. Whether this be accomplished by adding a particular Job Ability (JA) with a given cooldown, or a latent job trait, there are numerous ways this could be implemented.

Reasoning is that paladin has enhanced blocking rate job abilities (and spells), Rune Fencer has a heightened parry rate job ability, so it would make sense (if NIN is still considered a tanking job) to have something unique to the NIN job to achieve this.