Dragoons attack faster, have a damn near spammable aoe stun that chains to our heavy hitting TP Move (Heavy Thrust > Leg Sweep > Doomspike), Dragoons also can attack from a further distance outside of most close burst aoes like Ifrit's seer and such. Ontop of that whenever a Dragoon misses he gets to fire off a combo that can paralyze most targets while dealing good damage.

Monk put out insane ammounts of single target damage if played right and can drop some good debuffs with their combos. can virtually spam TP moves with fists of wind up and their TP gain. They make great support and heavy DD.

Warrior is only good for its hate building dmg and slef heals from crits but that would just cause chaosin the party with spotty hate jumping from one to another unless they hold back which defeats the purpose of being a DD if you have o restrict yourself from dealing damage because you pull insane ammounts of hate.

I think they all have their place in a party setup of every type and it should remain that way. I am constantly being forced to go DRG to LS events even though I'd prefer to go BRD or WHM because of my ability to throw out consistant dmg and not go beyond yellow hate after a few combos.