As an ex - 'World's Fave Airline' employee, I can confirm that they use Carmen for trip builds. However, it is 'cost effective' based provided that the the airline runs smoothly! (Now find me one of those if you can!) The downside is exactly what has happened at EZY; the aircraft/Flight Crew/Cabin Crew aren't rostered to follow each other around because they all have different cost restraints. The result - chaos when any of the three factors has a delay!
Let's consider keeping the system simple and logical. Surely the initial cost implications will far outweigh the actual cost of recovering the mess, not to mention hacked-off staff, both ground and air crew!