If your boss has a JAL credit card, and not a JGC member,
you had better try to be JGC member, not to try AA plat exec.
If you become JGC member, you keep paying JAL credit card annual fee, then you automatically get an oneworld sapphire membership(you need 0 mile for renewal). Even better, you need only 80,000 qualified miles for oneworld emerald status.
With sapphire leve status of JAL, you earn 100% bonus miles for JAL flight, and some kind of upgrade certificates that CX does not offer.

If your boss travels US a lot, AA is an option, but, travels within Japan and some longhauls, JMB is a good option, IMHO.