The QR flight is making money with the cargo on board only, technically it doesn't need any passengers to make a profit on the route.
I don't know where you got this assertion from!! Passenger aircraft should make money from the passengers; the cargo should add to that profit. It has always been thus, air cargo rarely makes money as a stand alone business for passenger carriers, if it did them BA would have a fleet of their own cargo aircraft, which they don't.
And before anyone mentions UPS and FedEx; they are integrators not traditional cargo airlines.