The whole line bidding thing is about conflicts. You can make many co nflicts with vacation, training, overlapping trips, etc......

There is somewhere around 20% less manpower needed for PBS vs line bidding.

This is the sticking point. Problem is FAs are willing to die on that sword and want everything other airlines get without giving up line bidding. Never gonna happen. Thats why they had deep sacrifices in their offer from company with keeping line bidding.