Whether it's trends, depth-chart movement or personnel changes, there are a number of different components that can affect a runner's value.
An effective quarterback isn't one of them.
Sure, Edgerrin James benefitted from the presence of Peyton Manning in Indianapolis, and life was much easier for Emmitt Smith in Dallas with Troy Aikman under center. But the absence of a reliable signal-caller is no reason to pass on an otherwise valuable back.
The proof of this statement can be found as we look back at some of the most productive seasons at the position during the Super Bowl era.