Please correct me if I'm wrong but US doesn't even provide seat assignments on *A partner flights do they? They give you a record locator for the other airline and you gotta' call them yourself. That's the way I've always done it.
So, you're wise enough to book this very sophisticated (and very difficult to attain) itinerary but you're not wise enough to know that you gotta call the airline yourself to request a special meal? That's inconsistent but what do I know?
Also, I don't think they owe you squat provided what the tickets are valued at in cash compared to the values of the miles for this trip. I strongly suspect they acted within the rules of the COC. You had the option to cancel if you wanted and you went ahead with the trip, right?
Give it up - this is the definition of a first world problem.