I think this topic ignores a key question that challenges the idea --

If you change the light party set-up to 1 tank, 1 healer, and 3 DPS and even out the queue-times a bit, how many additional tanks and healers will you lose due to faster queues no longer being an incentive to queue on those jobs?

Because a lot of players I know would abandon queuing as a tank or healer in a heartbeat if the DPS queue was reasonable.