There were 19 new college football coaches hired before Penn State hired Campbell (12 of those hires at P4 programs, 7 at mid-majors)
Campbell was not a serious contender - or even a consideration - at any of those other P4 jobs
After Campbell was hired, there were 10 more new hires (9, all but 1 of them, at mid-majors - 7 of those were replacing coaches hired elsewhere, and 2 who had fired their coach - and 1 P4 job, Michigan)
Clearly, for whatever reasons, he was not on anyone's "A List", and I doubt he would have been on Michigan's (Unless they simply ran out of options, which might be a possibility given the lateness of Moore's firing).
Plenty of "A List" coaches will - as is always the case - not be successful at their new programs (that list is loooooong).
And there are always folks who were not "A Listers" who will go on to find success (Cignetti? Dabo?). Time will tell wrt PSU/Campbell.
Campbell has been on A lists, for those willing to wait; he does not entertain openings until after ISU's season is done.

