This is about NFL coaching staffs...but it probably applies to CFB staffs, too. Why not?
Employing an elite, offensive playcalling head coach is the meta. I usually try to do rankings such as these in a vacuum, but there is no escaping the gravitational pull of an elite playcaller at the head coaching spot. Whoever calls a team's offensive plays might not be the single most important aspect of a staff's collective efforts, but it's definitely the aspect easiest to measure from the outside looking in. Securing a good playcaller as a head coach is the easiest way to ensure a functional coaching staff.Particularly in the case of elite offensive designers, such as Sean McVay or Shanahan, we know that they can scheme around talent deficiencies in a way that few of their peers can -- that's an enormous, floor-raising effect. This is a self-evident truth: O'Connell won Coach of the Year last season for a reason, folks.
Special teams coordinator and (most) positional coaches don't have an impact here. It's not because they don't have an impact on a team's season -- they absolutely do! It's just impossible to create a fair ranking of special teams coordinators from the outside looking in, where our data on special teams is very limited, and the lack of public visibility on the role makes it further difficult to riddle out a ranking.
Similarly, I'm sure there's a best wide receivers coach out there (and a worst, and a 19th-best), but I can't fairly make that ranking, so I tried to avoid it entirely. There are some positional coaches who are so inescapably valuable to their team and have been so over the years -- Eagles offensive line coach Jeff Stoutland and 49ers defensive line coach Kris Kocurek -- that their presence was baked into the rankings. But mostly as a tiebreaker, and only when their value was as plain as the nose on my face.
This is more a ranking of known to unknown rather than a ranking of good to bad. Thirty-two coaching staffs in the league, and while I understand that 16 of them have to be "below average" by mathematical law, it sure doesn't feel that way. I have the Bengals, Colts, Dolphins, Patriots and Browns as "below average" in this year's rankings, but not one of them is prohibitive to team success. In fact, all five have legitimately contributed to their teams overachieving in recent seasons.