Maybe it's just all about how player is builded. One DC with overall 40 mustn't be the same like another DC of 40. You can build players in two ways: similar vaules of mental, defence and attack skills, or dominating in one/two areas.

One time I had ST who scored a one goal in 5-6 matches. When I started to allocate all training points to physical skills, his game has visibly improved. Maybe it's an answer.