I wonder if it might work systematically - say someone has queued specifically for the Lv69 dungeon and reached the top of the waiting list. So the queue-filler looks at that, says "right, you need a tank" and puts tank in need until someone of the appropriate level joins the queue and can be put in that slot,*then* it shifts to calling for a healer next? And in the meanwhile all the ineligible-for-Lv69-dungeon tanks are instead piling up in the queue, and the system isn't looking at the lack of healers in the overall roulette.

That's the only thing I can picture as to how it might be doing that. I agree with the frustration of being clearly in need even though the game doesn't reflect that.