The thing with Mayo is he's never had to be accountable in any way visible to outside observers. He had a sweet deal as co-DC, getting credit when the unit played well, while somehow the blame went to Steve when it didn't.
There was one report of an anonymous person "in Mayo's camp" saying Mayo did/does most of the coordinating. Ever since, I've seen him placed on some pedestal where he is above anything wrong with the team. You can't draw a line between him and anything that can be critiqued because of the ambiguous nature of his role to us outsiders.
He might well turn out to be a great coach but his whole candidacy seems built by PR spins from the team and "Mayo's camp." Just an extremely difficult candidate to evaluate as an outsider. It baffles me to see people make definitive judgements on him (be they positive or negative).