That is not true. Stamina progress is minor with a nutritionist of the highest level. That's what people with experience said. I have had a level 3 or 4 nutritionist all the time for years. No player has ever improved in stamina. It only helped that they didn't lose skills often. But once in a few years it happens that a player loses a skill. With the highest level of nutritionist, it happens once every few years that a player increases his stamina. Cross training for 3 and a half years did not bring any pop up in stamina, and I have gym lvl 3.
I paid hundreds of thousands for nutritionist salaries and it didn't bring me anything. I have been paying a lvl 6 sports psychologist for years, I have paid millions for it and what happened when some players played 110 minutes for the first time? Their game shape dropped from 9 to 7, as happens to those who do not have a sports psychologist. I would understand if it drops from 9 to 8 because of a sports psychologist, but 7 is too much for that level and price of a sports psychologist.
But OK. I think it pays to have a sports psychologist and that having one brings good results compared to those who don't. I just think that when some players play 110 minutes once in a few seasons, that drop in game shape must be smaller.