I assume you're talking about his shiftiness with cuts. We've seen him to that before and I guess I'm optimistic that coaching can help him work that into how he runs. He also had a lot of rushes early in the season while Bell was OC, 49 with Bell vs 18 with Carey. The OL improved over the course of Carey running the offense and Lucas could have benefited from that.
Comparing someone to Barry would be very rare, dude was in his own lane.
Listed height and weight on their college pages:
Jaylin Lucas: 5'9" 170
Deuce Vaughn: 5'6" 176
Darren Sproles: 5'7" 180
Donnel Pumphrey: 5'9" 180
Obviously they don't always play at listed height and weight, and the numbers are usually buffed a bit, but I think it's closer than you expected. 15 pounds puts him in line with the rest of the guys and isn't inconceivable for a college player. He won't be a Blake Corum (5' 8" 213) or Cody Schrader (5'9" 214) but I think a comparison to the guys I mentioned is fair.
I really believe Lucas has the ability to take the next step at running back though I hope he can take a step both at rushing and receiving. How about we bring Dana Holgorsen in as an offensive analyst and have him tell Shanahan exactly how to make Lucas into Tavon Austin-lite?