I also have experience dealing with AA staff. I was travelling WTP/CE booking, booked with BA and the 1st leg was with AA. Allowance for 32kg confirmed with BA (both on travel docs and twitter message to BA) Tried to check in luggage and was told bags were overweight... got sent from one counter to another ( with luggage!) but it was still a case of “computer says no” and being told repeatedly that although it was a BA booking we were travelling with AA. It was a very frustrating experience but I stood my ground and eventually the bags were accepted. Arrived back to Glasgow and none of them turned up though😂
I think as long as you know your rights and don’t back down all will be fine!