Based on FIshers inability to develop offensive players, you are right.
I cannot think of any Rams offensive players that improved at all in the last 3 years, especially the drafted ones.
I guess you could make a case for Britt, but he was in the league for many years and I feel his success was largely a production of teams loading up to stop Gurley and knowing that the damage Britt was going to do wasn't enough to impact the final outcome. He received so much 1-1 or sometimes left completely uncovered that much of the success as a gift.