Using the labels major-national-regional in the most correct sense refers only to airline operating revenues. It certainly has no bearing on what those airlines do or where they fly (ie SWA, a major, does "national routes", as does nearly every "regional" these days; actually SWA flies more properly "regional" routes than many regionals!). The terms mainline-LCC-subcontractor make more sense. Until you get to RAH & YX; who is who in that unholy arrangement?