When you are hanging around, having positioned from your home base to ABC and have a 2 or 3 hour wait before operating a couple or 4 short sectors which may give you 2hrs 40 mins flying in a 10 or 11 hour duty day you will have time to reflect on what is fatiguing;duty hours or flyng hours.
The whole issue is too complex to have one basic rule for all occasions and situations;the west coast to Europe long haul crews will have different needs to the east coast or far/middle east long haul crews. The high density multi sector, predominantly daytime, european operators will have different needs to the overnight freight or charter crews.
Perhaps it's about time each operator was able to agree with the authorities,unions and crews a workable FTL scheme which suits their operation.