I looked up players that have posted a 4.5 ypc over their first two seasons that had 100-150 carries in that time (since Scott fell into that group). There haven't been a ton of guys in that situation (and that clearly has no bearing on how he will do in the future). But the names on the list are not world beaters . . .
Felix Jones, Ted McKnight, **** Bass, Ernie Green, Warren McVea, Clarence Davis, Justin Forsett, Rashad Jennings, Brad Hubbert, Barry Foster, Chris Ivory, Sid Blanks, Najeh Davenport, Cid Edwards, Troy Hambrick, Tom Moore, Albert Bentley, Joe Carter, LaMont Jordan, Robert Newhouse, Hokie Gajan, Jess Phillips, Russ Smith, Bruce Harper, Horace Ivory, Bill Triplett, Lionel James, Jarrod Bunch, Larry Johnson, Gerald Willhite, Tony Baker, Alonzo Highsmith, Frank Pollard, Curtis Brown, Robert Delpino, Kenny Watson, Kelvin Bryant, Correll Buckhalter, Ron Lee
The big name that jumps out is Larry Johnson, but the others have been mostly underwhelming when taken as a whole.
Scott reminds me of Mewelde Moore. Moore excelled when given the chance in either MIN or PIT. He's had 12 games with 100+ yfs scrimmage over his career but never seemed to earn more playing time and always ended up going back to being a role plater even after stringing together some decent outings in a row. Overall, I think players just get the rep for being a backup are are not really given a legit shot at becoming a starter.
Scott may fall into that category. In two years, he's only had 10 or more carries 4 times, and 3 of those were when Benson was hurt. If the Bengals really considered Scott as a guy to build around and their back of the future, wouldn't they have given him the ball more last year when they weren't going anywhere? As others pointed out, Benson got 86 carries over the last three games. Why would they do that if they wanted to consider Scott for the starting job? IMO, I don't see Scott's role increasing all that much and the main back will be Benson or someone else, but certainly we don't know that to be the case just yet.