Honestly I don't see why DPS are even complaining about the long queue times. Seeing as there are 9 classes with 2 of them are allocated to tanks and another 2 to healers with the remaining 5 allocated to healers. This leaves 5/9 or around 55% of the classes available to fill 50% of a group which is almost equal to the desired amount you would require having each role have equal proportions of available classes to available spots in a dungeon.

The problem lies in the distribution of the classes where everyone is rolling the most desired role which happens to be DPS or DD classes. Having a majority of people role DPS classes means that there are large amounts of people who are all queueing for dungeons at the same time for the same role which causes the bottleneck of supplying the other classes such as tank/healer to fill the last role required in order to find said run.