But in other cases they don't compete at all, and use codeshares as an alternative to competing. For example, AA doesn't bother to fly to Australia, and uses codeshares to there. So exactly over which routes is there big competition between AA and QF?

They already have a precedent for earning and redeeming exceptions related to competition (the US<->UK exceptions between AA and BA), so they could make similar exceptions for upgrades.

Also, a lot of these airlines don't compete very effectively (for committed members), because of how hard they make it for anyone who doesn't live in their region to qualify for any kind of status. If I travel to Europe some years but Northeast Asia other years, but every year I travel a lot within the US, exactly which other OW airlines besides AA are offering me any reason to go with them? I can't get anywhere on BA because I won't be going in their direction every year, and if they have the same "minimum metal" policies on JAL once they join then not there either if I won't be going in their direction every year.