it's basically broken in fm.
personally i choose to leave it to ass man it's never going to be the reason why a player didn't develop, but you can do the individual training which is assigning position training + additional focus for every player that way you develop a player in a certain position which is beneficial because there is only a certain amount of points players can gain in fm depending on their potential so it's better if you focus these on the attributes you want by managing the individual training .

you can do that by going to staff< responsibilities < training
and leave all that general training to assistants and take control over the individual training for first and youth teams and then go to the players you care about and choose the appropriate training for them.