I'll just try to keep this as un-emotional as possible while arguing my point.

You definitely have a valid argument, and indeed CX sees the benefits to having the alliance. Plus AA is simply a way bigger airline than CX due to all the domestic US routes, and those customers travel abroad. And that's a trade-off CX has been eager to make - get access to all those American customers coming abroad, and essentially using CX as AA's outsourced Asian capacity.

One thing interesting here is that AA today is not the same animal it was a decade ago. CX was effectively AA's outsourced Asian airline back then, and JL helped once it emerged from bankruptcy, although CX was still the workhorse. However, AA has made a very strong push into Asia the last 5 years from ORD, LAX and DFW. (UA used to be the dominant American airline serving Asia from the US, and Northwest from within Asia (later Delta) based at NRT.) But both of them have been given a run for their money by AA.

Interesting still, AA has even dared to go head to head with CX on LAX. I was at a group meeting with Slosar and Chu a while back when that launched. Someone asked a question, I forget who answered but it was damn clear they were not pleased at all. They also explicitly mentioned AA's expansion into mainland China as putting pressure on KA and hurting their feeder traffic to CX longhaul. If AA keeps up their expansion (pretty sure LAX-PEK launches soon), that puts pressure on both CX and KA, and I'm certain that changes some pieces of the calculus in CX City.

FWIW, another fellow at CX has told me the DFW AA route hurts CX by hurting some O&D Hong Kong traffic. Apparently HKG-DFW-NYC/ORD is actually a thing and takes passengers from CX.