PJ FLeck signaled the impending departures which he probably knew would happen early on when he said he fully supports coaches moving on to improve their careers. He himself was the beneficiary of the largesse of mentoring provided by Tressel, Schiano, and others.
It is rather unusual to have so many departures only after a year. All the schtick he has about HYPRR, FAMILY, and Nektons which make it sound like you are going to a comic book convention can gnaw on some folks possibly including assistant coaches..
I guess it is fine with me as long as he produces victories and don't wear down assistant coaches. His recruits seem to buy in.
I much prefer a rather stable coaching environment. At least, the Offensive and Defensive coordinators more longer term. If they have to keep changing all the position player philosophies and techniques every year or two, it might not bode well for recruiting or retaining players. But, you never know. Others college football teams probably are successful with the constancy of changes.
You win with talent, and then coaching. As long as he can recruit more talent, you have a prayer of winning more games than not. Coaches can do more with talent. You can only coach up less talented players to maximize potentials before it catches up with you at the higher level of B1G play especially when team depth is a mismatch with the big boys.