The system itself is actually a fantastic product.Left to do its job, with only the required FTL's and a max flying figure it would produce good results.
When you begin adding false restrictions like max days off in a row or, more particularly, something as tight as min 89 hours max 92-- then the system falls apart.
They could increase crew utilization (save money) and keep people happy--if they would let it do what it was designed to do.