There is a funny thing about averages. There are lots of ways to get to the same outcome. Singletary tends to do something like this (0, 2, 3, 0, 20) to arrive at a 5 ypc average when it might be more helpful to have (3, 7, 3, 8, 4) to arrive at the same ypc. Not to mention that McCaffery would be a significantly better receiver for a Bills team that likes to throw.
Also,CMC is the defense's first and second key on Carolina's dog water offense. In Buffalo he's not.