Staffing has never been a concern of UAL, nor of regionals other than ExpressJet. You bid on the flying even if you can’t staff it. So what if you cancel flight or have horrible performance numbers for a bit? As GoJet showed, it works. You get low upgrade times and eventually new pilots show up to staff the flying. The poor performance is forgiven and you get additional flying.
As for staffing the 550, that was an airframe designed to keep GoJet around. It just as easily could have been more -145 flying and, if the plug was pulled on GoJet by UAL the staffing would have come to ExpressJet. It wasn’t and ExpressJet will probably continue to have issues with staffing. Yes, hiring numbers have improved and hopefully will continue. But hope is not a method.