NIN became a tank in FFXI only because the players forced it in that direction. It was intended as a DoT DPS similar to THF. Tanaka just decided to roll with it instead of nerfing Utsusemi... SAM had intentions as tank in XI but keep in mind the only whisper of SAM we got was that folder on Soken's desktop which could have been anything. Gunner can't be a tank, at least not easily and we still need a new Healer so DRK fills the tank role probably without sacrificing the heart of the job since it's a natural blood tank. Even in XI it got heavy armor, high HP and potent absorbs and drains that allowed it to flex as a tank. So what if you can't pop six different DPS cooldowns and drop a 10k Guillotine or some crap like that. This direction means the blood magic isn't going to take the hit it did in XI where "balance" made absorbs and drains useless on endgame bosses.