Harmony,
I certainly hope that if you read all my threads that you will see that I don't just critisise.
Rostering is incredibly complex. You have only mentioned a very small number of the factors that have to be considered and that cause changes, so I have great admiration for rosterers. But from what I have seen, there are now more aircraft and more pilots but less rostering staff. They seem to have little experience and/or training, they are given less and less time due to constant changes to the schedule and they don't have any professional rostering software.
This is a result of short term cost saving and yet its knock on effects cost the company MORE. Flights have been cancelled or delayed due to mistakes, pilot utilisation is certainly lower than it could be and the CAD have now noticed that illegal rosters have sometimes been produced.
We all want improved efficiency and a profitable airline but the current management seem preoccupied with passing on the blame, making short sighted cost cuts and pressuring staff to produce more and more for less and less reward, rather than looking at how systems can be improved or listening to their staff.