These studies cannot exclude the fact that coaching changes often follow a dismal morale breaking season. I can see player atrophy in this case if the next hire fails to recruit and inspire. This leaves a HUGE responsibility on the AD not to botch the change.
These studies cannot exclude the fact that coaching changes include charismatic coaches moving up the ladder as it were. I can see player atrophy in this case as the perception to the player may be that he is being left behind.
There is no way treading water in a static pool prevents player atrophy.
jmo