Join Date: Feb 1999
Location: San Jose, California, USA
Programs: AS MVP Gold, UA MM, AA MM, IC Plat Amb, Marriott Gold, Hilton Gold, Hyatt Discoverist
Posts: 3,147
I think the FA could have handled this situation better.
Instead of barking at you that your bag was too big, the FA could have said, "Your bag might not fit in the overhead. If it doesn't, please let me know, so that it can be checked." There's no reason to make a big deal about a bag that so easily fits in the overhead, especially one that (as you say) meets AA's carryon requirements.
I hope you mentioned the FA's attitude in your letter. Right or wrong, there's absolutely no need for the FA to be unkind.