If AA had to switch a passenger to BA due to a schedule change or for some other reason that was not at the request of the traveller, they would not charge the YQ on the BA award.

As far as the OP requesting a refund for the YQ, I would probably press it. The OP could always use the excuse they "paid more," as in the YQ, to travel on BA (you like the seats, service, etc), and now won't be receiving those services.