I think "Toby" will get into a situation where he gets more regular touches than he did with the Vikings (not hard), but I would be surprised if he gets signed into a situation/dollar amount that makes him more than bye fill-in, occasional starter barring injuries/busts. not a terrible player or anything, but he has just been okay when Peterson has been injured.
Since he's been with the Vikings, he has only started five games with Peterson inactive:
12/20/10 vs. CHI - 16 carries, 77 yards, 3 catches, 18 yards
11/27/11 vs. ATL - 17 carries, 44 yards, 2 catches, 19 yards
12/4/11 vs. DEN - 21 carries, 91 yards, 8 catches, 42 yards
12/11/11 vs. DET - 19 carries, 90 yards, 3 catches, 19 yards
01/01/12 vs. CHI - 15 carries, 67 yards, 1 catch, 3 yards
TOTALS - 88 carries, 369 yards, (4.2 YPC), 17 catches, 101 yards
Small sample size, but those are decent numbers. 73.8 yards per game would equate to 1180 rushing yards over a full season. He also had a 109 yard rushing game on 11 carries in 2011 during the Redskins game in which Peterson tore up his knee. If you include that in the sample, his numbers jump up to 4.8 YPC and 79.7 yards per game. I think 4.2 is probably closer to an accurate reflection of his true merit as a rusher, but that's fine. 4.2 YPC on 250+ carries with 2-3 catches per game would likely make him a top 15 PPR RB.
On the balance, he has a career YPC average of 4.7 on 276 carries. He has 9 carries of 20+ yards, which equates to a "big run" percentage of 3.26%.
For the sake of comparison, here are the 2013 averages for last year's 200+ carry backs:
CJ Spiller - 4.48%
DeMarco Murray - 3.69%
Alfred Morris - 3.62%
Frank Gore - 3.26%
Matt Forte - 3.11%
DeAngelo Williams - 2.99%
LeSean McCoy - 2.87%
Adrian Peterson - 2.87%
Reggie Bush - 2.69%
Ryan Mathews - 2.46%
Jamaal Charles - 2.32%
Chris Johnson - 2.15%
Maurice Jones-Drew - 2.14%
Knowshon Moreno - 2.07%
Zac Stacy - 2.00%
Marshawn Lynch - 1.99%
LeVeon Bell - 1.64%
Eddie Lacy - 1.05%
Fred Jackson - 0.48%
Ray Rice - 0.47%
Rashard Mendenhall - 0.46%
BenJarvus Green-Ellis - 0.45%
I'm not going to suggest that this stat is the perfect indicator of RB performance. It's highly prone to variance and it only speaks about a back's big play ability, not his consistency grinding out short gains. I think you'd also expect a backup/COOP back to have a higher big play percentage than a workhorse who's carrying the ball 200+ times if all other variables were equal. However, there does seem to be some correlation between these numbers and talent. The fact that Gerhart has been breaking long runs at a rate that's equal to or greater than most of the backs in the game is another positive sign for him.
I think the people who automatically assume he's just RBBC fodder are a little off base. It might play out that way, but it might not. Nobody assumes that this year's highly-touted rookie RBs like Hyde, Mason, and Hill are destined for committee situations. Gerhart was picked approximately where those players figure to go, he was just as dominant in college, he has arguably better overall athletic tools than any of those guys (he's 230 pounds [the weight of Hill and Hyde] with 4.50 speed [the same time as Mason] and a 38" vertical), and he has already demonstrated some degree of viability in the NFL (high career YPC, respectable showings in limited starting chances, and hints of explosiveness in his efficiency metrics).
In my opinion there's an inconsistency with the lauding of players like Bell/Lacy/Stacy/Mason/Hyde/Hill and the simultaneous insistence that Gerhart is probably destined to be a committee back at best. I don't think there's much concrete evidence that he's less talented than those guys. I think the impression comes mainly from the fact that he's been sitting on the shelf for four years while those other players are either fresh out of college or have benefited from being in the shop window as starters in the NFL.