Good point. If Dennison were to bring the same zone scheme to Chicago, though, the Bears likely would be able to move away from Forte once it became financially worth it to do so. Other than Portis, I'm not sure Shanahan has ever had a "great" back, but he always has a really good run game. And while I think Arian is a talented back, he's not nearly as good as he's been in Houston. With that scheme, you can go cheap at RB and still be productive, opening you up to spending more money elsewhere. I think that even though his was short-lived success, the degree of success that Terrell Davis had would lead me to consider him a "great" back. He averaged over 1600 yards per year (including a 2,008 yard season), 4.75+ per carry on 330+ carries per year before his knee exploded. The caveats of him playing with Elway and some pretty talented receivers apply, but I think it's enough to consider him a "great" back.