Carson is the type of RB Pete covets. He runs hard and delivers blows to the D punishing them when they tackle him. He'd rather deliver a blow and hit the defensive player than step out of bounds. Naturally this style leads to injury.
Carson has been a hugely successful 7th round pick for the team and fits the physical play mentality Pete would prefer. The team is much better on O when he plays and can be counted upon.
The team has trained Carson to not drop the ball which was an issue to start with and that caused him to be benched early for short periods. He energizes the OLine and the O when he runs hard and is good at conveying short yardage situations. I think Aros has got it dead right above here and the team will of course try to keep Carson, but his injury history certainly reduces his market value and he has performed well enough to be paid well but perhaps not as much as he thinks he should.
So far little I've seen from Penny indicates he could be the lead back and he's had injury issues completely inconsistent from his college history. The others except Hyde are just guys and none but Scarborough hold much interest to me. Scarborough could, if he can return, be a punisher. He was running hard against AZ and certainly caused me to be disappointed when he got hurt.
Money will be the deciding issue for Carson next season as to whether he remains on the team.