American AAdvantage -> JAL Mileage Bank?

Reposting as my post somehow seems to have disappeared into the ether.

I've been a lifelong AA flyer like my dad, have racked up a lot of miles, and also have the AAdvantage credit card back in the US. Family is mostly in the US (LA and Boston, some in DC and SF area also), and I try to go back as often as I can. Most American and JAL flights can accrue miles more or less interchangeably, on one system or the other, though there are fare codes and the occasional codeshare that make things not translate. However, while I am a US citizen, I'm in Japan for the long haul, having just started a new job, signed a 2-year lease on an apartment in Tokyo, and in a pretty serious relationship with my girlfriend who is Japanese. And she happens to work for JAL.

I know that miles cannot be transferred from one company to another even though they share the OneWorld alliance connection, though the AA Platinum status that I somehow achieved through flying for work last year translates to OneWorld Emerald status on JAL. That makes it pretty nice, as JAL is much more generous (and high class in general) with service perks in comparison to American, and it shows through even more when you have the coveted Status.

I read and speak Japanese fluently, but I have heard from multiple sources that US mileage programs make it easier to earn and use miles in general and JAL's website is out of the stone age in comparison to AA's US site. That being said, recent news has indicated that JAL is updating their system, and American airline companies are starting to make it more difficult to earn and use miles. Moreover, now that I work full time (and have a personal incentive to learn more about JAL), I have discovered that JAL's JALpack tour deals make it pretty easy to get away for a weekend or long weekend, and are much more affordable than buying a la carte tickets and hotels. Also, while I got a Rakuten credit card, Rakuten is annoying as hell with their Super Points, and I hear tell that even just being the bearer of a JAL credit card is enough for the JAL staff to treat you with some kind of status at the airport, never mind other opportunities to use the card while being in Japan. So I am strongly considering getting a JAL credit card pretty soon.

Can anyone offer some insight on how to approach airline loyalty when shifting focus to a new carrier within the same alliance? Is it worth it to make every effort to migrate to JAL? Or stick to American? I learned a few years ago that there are tangible benefits to focusing on one or two carriers and getting there credit cards, and while I don't fly a ton, I do fly more than most. There are benefits to both systems, and while it seems like a very natural and sensible thing to do to focus on JAL and get their credit card (especially considering my personal connection), I can also think of benefits to keeping focus on American (namely, keeping status and the credit card(s) there... the relative ease of using the award booking system may be negligible, but there is the Million Miler thing to aspire to someday also). Can anyone offer insight on this?