Toney's age, eating, lifestyle, and non-running have finally caught up to him.

It wasn't Billy Banks fault, I don't think.
Billy was brought in the team as the "new edge" Toney would need to surpass the GIANT Nigerian Peter. Just as Erik brought in Velocity, Vargas changed his trainer, so did Mosley (Shane is doing good now though), Campas drank magical juice before the Oscar fight. It's just something boxers do in times of need, they look to other options to help give them an edge in times where their careers seem to hang in the balance.