You don't seem to get the point. Your definition of "good" is not everybody's definition of "good". Some people will refer to an 8/10 as good, some people refer to a 3/10 as good. Some people don't even think in terms of 1/10.
My definition of GOOD(in this situation) is a player who showed that he is a very strong link in United. I don't think Valencia of yesterday reaches that level, he would not be a very strong link for us even if he had constant games like yesterday. In fact if he played every game like he did yesterday, he would be the worst player in our first eleven bar possibly the LW position.
If Valencia played for Aston Villa, I would also deem him good yesterday and would praise him for his display.
I should again add though that I agree Valencia was good for being him - this season.