Most teams in the "pretty good" range play about 4-5 "real" contested games a year, right? Many of us look at the schedule and see 7 or 8 near certain wins preseason (unless the wheels fall off of course). So, let's say a team is at least pretty good, and manages to win those 7 games and then goes 2-3 in the 5 contested games. So, you're 9-3, and perhaps no better than "pretty good". On occasional years, the same teams is 3-2 or even 4-1 with a break, and they end up 11-1 looking like world beaters but may not have beaten anyone really (they tend to get bulldozed in a bowl game).
Putting aside recruiting, how many games a year will a good coach win that a mediocre coach would lose? Two?