Player performance in friendly matches may be used as reference but ought not be relied on to evaluate players.

I used to have a 2 star goalkeeper. I used him to fill various positions during friendly matches. When he played as ST/AMR/AMC/AML, he was always a very good and probably the best superstar scorer in my team. I cannot guarantee that he cannot be good scorer in official matches as I never tested but I cannot believe this will happen.