We are talking about primary roles here, BLM is a nuker and WHM is a healer, buffs fall under healing and light enfeebling (uh sleep?) doesn't really count as a huge secondary role.
Aside from that, I tank almost everything on my Thief. Thief is a DD, a Tank, Utility in TH, one of the few ability to reduce hate (WHM don't regain hate that quickly, BLM can deal more damage when a THF steals enmity even if it only lasts for 3 nukes or so before they start getting beat.) Thief is a great soloer, can hold mobs very well with evasion, in the past was a decent puller, can enfeeble with bolts (zomg look, same thing you did for BLM). etc etc, stop trying to seem like THF does nothing but TH.