There is a bit of truth to what the OP is saying. US has always been the ugly step sister of *A. Consider that AC (which is next door neighbours with US) has never completed a codeshare agreement with US and the two airlines have a poor record with passenger transfer while AC has codeshare agreements and enhanced passenger transfer functions just about all other *A airlines (ther might be 3 regional airlines on the other side of the world that AC does not have an agreement with).
If I were to catagorize the present relationship as follows:
1. UA-CO
2. UA-CO-AC-LH-SAS (Anti-trust immunity partners, revenue sharing, codeshare).
3. Rest of *A
4. US and the *A regional airlines.
There is a lot more in the pipe for the antitrust immunity partners that will benefit their elite flyers to the exclusion of US. I would strongly advise any remaining US elite flyers to status match over to UA-CO.