Top RBs are more valuable than many WR1s.
And frankly, there are 30 WR that I truly call WR1.
Does it take into account that the likelihood of your QB being injured increases when you can't rush the ball?
The RB affects the game in too many ways (domino affect). Now, I will say a RB that can run inside/out AND receive adds value. But that is because it allows the OC to disguise more plays because of a double threat.
But maybe this comes down to a definition of value. Mine differs from PFF. Vastly.
