In my experience,whater little I have had, 5* players take time to show their worth. Like my 5* AMC did nothing in his first 3 matches, got injured and after recovery, now he has a goal a game average with high avg rating. Same with my 5* ST Mattis who was avg first 4-5 games and now scorers every match and yesterday got a hat trick. And my 2 match old5* ST did nothing in his first match, yesterday he scored one and assisted one. But the defenders seem to start performing quite quickly, right from their 1st match. As for GK, some prove pathetic no matter what Q they r. My 5* Keeper Graikos was useless, bought another one who is much much better. Graikos is 22 yo and has M.V of 7.2 million. I am currently training him and will sell him at the end of the season.