AA PLT status will give you lounge access on domestic flights connecting on same day international segments, though not on separate USA domestic flights. Seven AA codeshare round trips LAX-MEL (at just under 8K miles each way) in one (calendar) year will provide EXP status. The same on QF flight codes will be 45 status credits each way - or enough for QF Gold or AA PLT.

Seven in Y+ (QF fares only) would provide QF Gold. Two in Y+ (plus a couple of short flights) would be AA PLT.

In seven business class flights either program will yield OW Emerald. In any case your issue will not be lounge access but who provides you with better irregular ops support and better awards / upgrades. Remember awards / upgrades on USA-Oz flights are difficult (though not impossible) to find even for QF PLTs.

Happy wandering.

Fred