It is also worth remembering with codeshares etc that you are a customer of the marketing carrier, not of the operating carrier. Outside of the actual transportation and in flight service, you are subject to the various policies and customer service gestures of the airline you paid. I have no idea in the case of AS tickets, but you may perhaps have better cancellation options etc than if you'd booked with QR, as well as paying the cheaper fare. The operating carrier will also likely be receiving even less than the $3,000 saved, after AS take a commission or admin fee.