It also comes down to the play calling as well. The Bears telegraph too many of their plays.
A solid O-line with some aggressive play calling makes RBs and QBs much better. If Rex can just play pitch and catch, he is pretty damn good, but when he can't even get to a 3 step drop before having to bring the ball down, something is wrong. If Benson gets through the DL, he normally has some pretty good runs. The problem was he was almost always hit at or near the LOS.