Mosley did not accomplish what he did because of steroids. It was because from even before he could walk he spent all day, every day in the gym. Before he could walk, he sat in a basket and watched his father train fighters. At 5,6 years old, he was hitting the bags and learning how to move around. Check the record he had at age 12.
What effcts steroids have on boxing is debatable. Shane, a guy that had boxing bred into him as much as is possible, was still only 'real good', well below guys like Billy graham and fritzie Zivic, much less the guys like Napoles and Armstrong and Robinson.
You ought to give it a rest and think on it. Think on what it takes to be an amateur champion on the level of Shane mosley, or the effort it takes to learn the moves he made during his lightweight reign. Steroids don't teach you skill, and boxing is a skill spot.