Holmes wasn't a proven feature back when Larry Johnson was drafted. LJ was on his rookie contract for the most of his career until Holmes got his with injuries.
Michael Turner never got enough carries to even be worthy of a conversation. He shared the load sorta with LT, but LT was always the money man.
Bettis was one the downside of his career when Willie Parker was drafted. It wasn't about sharing the load.
Tiki was the feature back meaning he was better than Ron Dayne. Jacobs was drafted the same year Coughlin was hired, I believe. Tiki's fumbling problem went away and he became a dominant back.
By comparison, Barber started his rookie year due to injuries by Julius. Julius came back, Barber went back to backup. There was a changing of the guard, or at least the thinking, in 2006. Barber became fan favorite, but he still shared the load more than anyone considered a feature back.
This would be Barber's first year as feature back. I'd really like to see him show what he could do as true, lead dog.