Here's the thing about the 4 days off. Let's run a scenario in which 4 day off waiver is not possible under PBS. What happens then? Would you have been able to get the perfect line you wanted for June? I wager the answer is no because it would have violated the 4 day off clause at one point or other. As soon as the schedules aren't premade the 4 day off clause becomes meaningless because pilots don't care about the 4 days off as much as they care about other schedule objectives.

What would have made sense is to trade the 4 days off for a higher number of monthly minimum days off.