> the famous United case where the senior was dragged off the plane screaming and kicking was not on United but a low cost fully owned subsidiary carrier of United

United does not own Republic Airways and they are not a subsidiary of United Continental Holdings (United's parent). Republic is its own airline operating flights under contract for United, Delta and American.

The legacies by and large do not own the regional carriers, nor are those airlines intended to be low-cost carriers. The differences primarily lie in the aircraft operated and result from union contracts that inhibit the legacies from profitably operating smaller (non-mainline) aircraft.