user999991 you have made several assumptions

Firstly that your mileage balance impacts your place on the WL (which as others have said is clearly incorrect). Secondly that those who were upgraded in flight would be lower down on the WL (I don't think you can assume any such thing with confidence), and thirdly that you were actually added to the WL (which may or may not have been the case)

Whilst I might also have been a little peeved, i'm not sure you have any compelling evidence that UA messed up

Jeff