Thief:

Steal potion: Steals a potion-like item and uses it to recover slightly pty members HP.

Steal ether: steal an ether-like item and uses it to recover pty members MP.

Steal boost: steal a boost potion and uses it to apply a random boost effect to pty members.

Trick attack: attacks critically the target and transfers the hate generated by the attack to the person between the player and the monster.

Evisceration: Finishes the rouge attack rotation and applies bleeding.

There you have, a thief job with steal abilities for those who want a thief and a hybrid support/dps class (which Yoshi already stated they want to implement) for those who oppose to thf. I'm not telling SE to use this idea, i just saying that if a part of the community want a thif job even if it's only by name the can do it in very different ways w/o repeating a job, this discussion about if it's thief or not is a bit pointless, if ppl want a thf, SE will make one, because this is a business, and nothing gives more money than listening your customers.