I'm just playing devil's advocate and arguing what they would argue so please don't take this as what I think.

Is it fair to that captain at Mesaba that may be junior to a Comair FO in terms of DOH to be bumped out of his/her seat because he chose to go to Mesaba as opposed to Comair? That Comair FO could have went to Mesaba and been in that captain seat just as easy if it was all about getting an upgrade. In their eyes (and the eyes of an arbitrator, just as in the USAir/America West case) it comes down to career expectations. Could an FO at Comair reasonably expect to upgrade in 3 years? That answer is obviously no. Could an FO at Mesaba expect to upgrade in 3 years. That answer is easily yes.