If you use oneworld website and just have first leg BA or AA metal doesn't it automatically have those carriers be the issuer? I have only used the older version (pre 2020) and always CX.
Hear anything about JAL? i see you have location as nrt/hnd
Noted on the mile limit, thanks
If your first leg is AA or BA then the online tool would very likely ticket it on them, my understanding is that it tickets it on the first carrier.
Personally I wouldn't ticket it on JL. It's not that they are incompetent, generally I find them to be pretty good but things take a long time. Japanese very strongly stick to the rules and will research them like there's no tomorrow. You won't get a JL agent to bend the rules for you if that's something you ever need. But my real point of hesitation ticketing a complex ticket like RTW with them is the English level isn't great on average and it adds unnecessary communication barriers. Also their call center hours in the US are pretty ridiculous and in Japan they don't have a toll free number, so gets expensive to call them.