Thanks for sharing your experience.
I'm not sure if this suggests alliance wide policy here. If anything, it only reinforces AA's policy on
separate ticket and illustrates AA failing to rebook you properly.
AA caused the misconnect. AA was responsible to rebook instead of getting QR. Seems like QR agent was correct in sending you back to AA.
Was the award ticket for LHR-DOH redeemed with AA or QR miles?