BA allowance applies since that is the most generous. I had some (QF) agents argue before but the BA MMB print clearly says (at least said) most generous applies.

Having said that, I agree with the above - has somebody checked your hand luggage on AY? I had 3 roller bags totalling about 60kg stacked on top of each other when I moved back to Finland and nobody cared at BKK. Same on EK a month prior. I dont support that but I could have never paid the excess. Hated hauling around that junk.