I thought a little bit about the new staff. The idea is cool, other games have a similar system. In my point of view, this addition can change the game drastically. Two groups of managers will benefit from it more than any other.
1) U21/NT farms
2) veteran player teams
1) U21/NT farms
If you have enough money, like some Utopia teams, and you only exist to push out U21 players or start training NT players, this is a wet dream. At this stage you need two of the three secondary staffs. The youth trainer and the nutritionist. Thanks to the youth trainer you will boost the first two seasons of training. You can push OD or JR (imagine this with a <185cm player) or go for six guys and 1on1. And at the same time, there is a possibility to train stamina. Even if the effect of the nutritionist is very small and you get one up per season, that's one week of training which you can use for something else. You would need the best guy only until you reach the needed stamina level and after that you can switch to a nutritionist, who just keeps the level.
2) veteran player teams
The second group is the heavy competition fraction. Teams without trainees who compete for the Div. 1 titles and run the BBB. Here you would need the sports psycholigist and the nutritionist. I could imagine that the sports psychologist can keep a smaller rotation in a good game shape. Your minutes will go up, but he will manage it. And at the same time the best nutritionist could improve the stamina, which will have again a postive effect on the minutes. These two could really work hand in hand.
This combination could reduce the need for stamina and game shape training. It would give you more room for free throw (which is influenced by stamina) or some "into the cap" training.
So far my thoughts and opinion.
And now back into hibernation
