Hey El-Duderino ,
my brother also has a team and recently decided to move to classic 4-3-3 (4D-3MC-3ST) and set mentality to defensive , but it doesn't work as smoothly as you described so i wandered what were your other settings (man-to-man/zonal, type of passing, mixed/through center, tackling and so on....) .
do you play with any arrows ?
i useally play with 5-6 other formations so couldn't really advice him on the matter...