Former XJ here. Mesaba was operating under a bankruptcy contract that was still better than Colgan (they didn’t have one yet because they had just voted in ALPA shortly before). Mesaba was losing airplanes when they were sold to Pinnacle and Colgan was taking deliveries of new Q400s. The argument was that a pilot going to Colgan had a better career expectation of moving to the left seat quickly. It worked in the eyes of the arbitrator (who also dabbled in magic on the side).