My experience has been that when traveling on *A partners, it makes little sense to complain to UA if you are seeking compensation as they will respond to you politely to seek redress with their partner.

What writing UA does is make them aware of the possible mistreatment of their elites by *A partners which, if there is ample evidence of it, may probably lead to some service adjustments/improvements the next time the *A gets together to iron out issues. If no one rocks the boat, member airlines may not fully know the extend of the problem.

As for you issue, I would take it up with US but still cc: UA CS on it.

Good luck.