If you increase the number of DPS you also need to increase the number of healers to heal them.
The reason queues are so long probably has more to do with other factors. One being the lack of a real catchup mechanism, means you have people spread out over a variety of wings. Another is that the way loot drops work even if you are all caught up to the most recent tier you stop needing to run certain wings based on what drops you get and that differs from player to player. Whether or not a wing has many good drops for a healer will have a very strong influence on how quickly healers move past and stop queuing for that wing. Another is that some wings are unpopular due to difficulty.
If you could get players focused on queuing for the same content many of the queue length issues would go away.