off play calling to ARod and Fesi). He's great at player development (look at the O-line). He's great at doing those things which are MASSIVE components of being the CEO of the football team.
Very many coordinators struggle making the jump from OC or DC to HC because they are great at Xs and Os, but not at actually leading and running a team. I am one who think Grimes would be a better HC than an OC.