The DPS queues are caused by player base. Its not something the game developer can easily fix at this point.

Changing 4 man duties to 5 man to have a 3rd dps will help for all of maybe 1 month before queue times go back to what they are now. The reason being it seems a lot of you fail to realize a number of tanks and healers queueing these duties are doing so because it has a shorter queue time on those roles. If the DPS queue time goes down they will start queueing as DPS because its their preferred role or job and the role distribution in player base will shift to a higher DPS percentile.