had you been booked on BA68 you would qualify but being booked on an AA flight number and on AA paper you do not
No, regardless of the marketing airline it is the operating airline that counts here. AA Metal JFK-LHR but BA or IB flight number, the Regulation doesn’t apply.
This, of course, is insane because the marketing airline is who you have a contract with.
But even though the Regulation may not apply the airline still owes you a refund between the fares. You will be surprised how little this can be.