Great running backs, their greatest attribute is their field vision and the ability the see the holes where other running backs don’t.
I do still stand by my premise that those are skills that have to be present, and can't be coached beyond a point of diminishing returns. You're not going to coach an armadillo into outrunning a gazelle. With Tony Dorsett, the joke was his field of view was so good he could see his own ears.
A coach told me though, "you can't coach speed or size." If a guy doesn't have vision or cutting ability coming into his second year, he's not going to develop it. Now, sometimes, a back is stuck behind a lousy line, and a change of scenery can make all the difference. I've always wondered what Sanders or Sayers could have done on a team where they weren't the only weapon.