Barry Sanders is a perfect example, and Barkley has looked a lot like him through his first few games. Sanders could run for 150 yards on 20 carries in a game, but when you looked closely at his games you'll see that he was very ineffective despite all those yards. In his typical 150-yard game he'd have two long runs of 60 yards each, then just 30 yards on his other 18 carries. That's an awful recipe for an offense in the NFL, because the team can't run a ball-possession offense and usually faces situations of 2nd-and-9, 3rd-and-7+, etc.
It’s true. Philadelphia was very much “Running Back by Commitee” last year. Ajayi was the flashy runner. He’s hurt this year. But they very much miss the tough yardage Blount got them last year.
Detroit was very much 1-dimensional. Sanders faced 9, 10 men in the box often. That will make you the kind of runner you aptly described. Had they any kind of passing attack, Barry would have been more effective.