Mayo clearly lacked Xs and Os acumen, especially for someone in the position of head coach. You needn't look any further than how badly the defense regressed on his watch. Covington was clueless how to adjust scheme-wise for personnel shortcomings both in-game and between games. As a supposed "defensive specialist," Mayo SHOULD have been able to help him out but you're talking about a guy who -- like his DC -- had no experience calling a defense (and still doesn't).
BB didn't tutor him the way one might assume. He was a linebackers coach then briefly shared DC duties with SB. SB did the defensive game planning with his dad and called defenses on game day, Mayo ran the meeting room. As for offense, well, there's a reason he dubbed AVP "offensive head coach."
Mayo was so unprepared for the job from the standpoints of both experience and working knowledge, Kraft should've had his head examined for handing him the job.