Depends what they do with Yearby moving forward.
If they pack the weight on to him like they have Duke then I can see him losing his effectiveness.
He's not a workhorse back, but he'll keep those chains moving all day if he's part of a rotation.
Maybe both. They'll put some weight on him but he may still end up best as a rotation back. He's a small guy frame-wise.
On the weight thing, the component people never talk about is that it's best for the PLAYER to gain weight in terms of their future. The NFL isn't clamoring for 175 lb scatbacks. It's hard to be a high draft pick below 200 lbs. If a small back wants to maximize draft status, you need to get to that 205 lb range and hopefully retain some of the quicks you had at 175. Ameer Abdullah did the same thing.