Run game excellence isn't just about the players, it also goes back to the philosophy of the offense these guys are in. So Williams for example is going to be limited by the fact we're a team who runs it to mix it up, rather than a team that works hard to dictate the run to free up our pass game options like SF does.
McCaffrey for example benefits from that to some extent. He's a fine back when he's healthy, I gotta admit that. But he's not in Barkley's class, to my eye at least.
Another back who should continue to rise is Hampton, simply because he's going to get a shit ton of work and focus on that run game by Harbaugh with the carpetbaggers.
An example of a back I think will fall is Henry, who will face defenses loaded to stop him I expect, due to transition from the other Harbaugh to the new staff. I have a feeling they're gonna have some difficulties and that may end with a change at QB at some point.