They probably need to introduce more options for tanks/healers, or to make their play style more interesting.

As it stands, pre-30 here are the class compositions:
Tanks - 2 (Gladiator and Marauder)
DPS - 5 (Lancer, Pugilist, Archer, Thaumaturge, Arcanist)
Healer - 1 (Conjurer)

Post-30:
Tanks - 2 (Paladin and Warrior)
DPS - 5 (Dragoon, Monk, Bard, Black Mage, Summoner)
Healers - 2 (White Mage and Scholar)

Basically, what I'm trying to say here is that there's way too many DPS classes, combined with the fact that DPS classes are by far more popular than tank or healer classes, we're looking at a 1:4 ratio for Tank + Healer vs. DPS (DPS count increased because of the fact there are more DPS players than tanks or healers) - just something exaggerated, I don't have actual figures, but it's kinda something like that. There's an overpopulation of DPS, compared to tanks or healers, which also makes up 50% of a DF party.

As far as I know, it seems to be a common MMO design problem. Best option for a DPS would be to find a tank/healer to party with really...