I think that BWI was one of Piedmont's hubs and a considerably sized one at that. It's true though, BWI is barely more than an outstation, with US flying routes that don't compete with SW. I think another reason that BWI shrunk in operations is because of the termination of MetroJet flights. Most mainline flights had been replaced by metrojet flights at BWI, and then after 9/11, US retired the 737-200's and the metrojet system was no more.