Sports psychologist is a very strong feature, that any team with any winning motivation should have.
There is a consensus on how powerful that is.
Alright. But there is nothing more powerful than managing your minutes.
I've never had and probably will never have a psychologist and my game shape has never been an issue (and I play intermitently since season 2).
Currently 7 of my utopia top-10 salary players have game shape at level 9, 1 has level 8 and 2 have level 7. Considering my two teams altogether, from the top 10 players 6 have GS 9, 3 have GS 8 and only one has GS 7. It has always been like this.
But ok, since I've never had a psychologist I cannot tell about the impact in the GS on players who get gung-ho minutes during a week. If players can play 80+ every week and consistently get high GS with a psychologist, then it can be really worthy. However, if your guys play "normal" minutes, your game shape will be under control without the need of anything else.