I agree with mctones. Not about Benson, but about efficiency. It's all about efficiency in regards to a rb.. Some backs will have more yards do to the system they play in (broncos). More touches = more yards, so yardage is not a great indicator of a good back. efficiency from the point of attack, ypc and successful offensive touches per carry are.
NFL teams looks for efficient backs, backs that consistently have plus yardage runs, and a good ypca compared to the amount of times they touch the ball. Guys like my boy Maroney : )
185 touches 837 yards 4.5 ypc avg... Compared to a back like Addai getting 261 touches for 1012 yards and a 4.1 ypc avg. maroney was one of the top backs in the NFL when looking at successful runs, and efficiency. That said, both backs played in high power offensive system that liked to throw the ball, but are more efficient than runners who touch the ball more times, and focus on running the ball.
Benson is not a terrible player, he is a disgruntled slacker, who had no offensive game to help him out. He's not good, but he isn't as bad as you think he is.