I do get what you're saying. I really do. However, I don't believe a team should replace its RB only because the RB's production could possibly be matched by another RB.
I like Mattison but he is not Cook. We would have retained Cook had our cap situation been different. He did not want to take less money, which I understand. JT is younger than Cook and he was the best offensive player on the Colts. I hope the Colts retain him. It will maximize Richardson's and the team's chances of winning.