I like this "we have enough tanks" argument that crops up, as if 3 melee DPS isn't enough either by this logic. No, adding a 4th positional-based DPS would certainly make for a vastly different playstyle against NIN, MNK and DRG...

If people want SAM as a DPS (even though it's unlikely; the job was close to being HW's tank over DRK, losing out due to not being compatible with the expansion setting) that's one thing, but trying to argue that 3 tanks is enough yet a 4th melee wouldn't be overkill is silly.