Obviously thanks to the guy for chipping in and all the best to him in the future, it's nothing personal.
But to kinda come at it from a different angle, forget the whole OC, playcalling piece of it for a second.
To really succeed in football in the 2020's, even playing BertBall in the B1G West, you need excellence from the QB position.
However one may assess Petersen's OC career, whatever success he's had has been working around pedestrian QB play, even with Gardner Minshew in the AAC. Good things are not coming with him as your QB coach/developer/recruiter in the Big Ten, and if it's not going right at that position, you're fighting with two arms behind your back.