Whether or not a running back is pivotal to a team doesn't mean that they will be selected as such. For example, even though most people would want to draft an RB late, because other people are drafting one early, means that most fantasy football leagues involve taking a RB within the first two rounds. These drafts are highly reactionary. For example, I changed my first round pick based on who RSFFL took in the first round. And that caused a chain reaction amongst QB's. I doubt that the first round would have looked the same if the first few picks were Chris Johnson, MJDizzle, Fumbles All Day etc...