From another thread:

Quote Originally Posted by RaideDuku View Post
Why two DPS?

Tanks - WAR, PLD, DRK
Healers - WHM, SCH, AST
Strength Based DPS - MNK, DRG, -SAM-
Dexterity Based DPS - BRD, NIN, MCH
Intelligence based DPS - BLM, SMN, -RDM-

Now we got 3 of each. Know that's not going to make most people happy, but I know at least a couple of people that'll be thrilled there's a proper sword slinger DPS, now. Two, actually, if you count RDM being a sword slinger.
The players have style options now with split parity across the board. This is a good thing. Honestly I was initially disappointed with no tank, but once I thought about it, I was glad that SE chose to try to clean up and bring identity to the Tanks and heals we have to try to make them more fun to play. PLD needs some attention, so I don't want SAM tank stealing that spotlight.