The real issue and why we have a seniority based upgrade system is safety. There is enormous pressure to get flights out and moving on time from all sides of a airline operation. The most important role of a Captain is as Delta tells their new Captains "Making the tough Call". That means shutting down the flight when safety is not what it should be. Without a seniortiy system pilots who make those kind of calls when needed would quickly find themselves back as First Officers while pilots who would fly aircraft not in the proper condition for that flight or into conditions not right for that flight would be upgraded. The seniority system gives you the ability to say no and never have to worry about how it might effect your career. Its the key issue to a safe operation.