I have a lvl 7 nutrionist now for 3 seasons on my Utopia team and my main team.
one with a fitness trainer, the other not.
Only the one with a fitness trainer has given me 1 pop on stamina over the three seasons.
I have had no drops in stamina since I have the level 7 nutrionist.
In my view the money is not spend well on a nutrionist, but for the sake of my experiment I will keep it running for the time being.
Only in the dark, we succeed!