I don't think ive ever had a good MC. They either have an average rating of around 6.9-7.1 or they are absolutely rubbish. I've had 2 scout players similar to yours. I gave them good runs in the team, played them in their right position, kept they morale and condition very high but both their average ratings were 5!!!! And that was in teams that won the league very easily and the rest of the team were over 7.