I, too, don't understand why the 12 hr rule would be bad for QOL. Couldn't mgmt just make the duty days more efficient/productive so that we fly the same amount as we do now but with the shortened duty day? Or is that too much to ask for? Because flying 7 hrs a day doesn't tire me out - 14 hr duty days do. Personally, the optimum work day would be a high block with short duty day which would also result in a shorter work week due to the 30/7 rule.
Some airlines contracts already have a limit on duty day, does that affect the quality of their schedules?