Heng was not a hero. The fact was his cowardice and spinelessness were rare traits in team China. The former Heng was not a person worthy of being trusted despite the exceptional archery skills he possessed. The two mental flaws turned him into the most unstable person in the team if problems arose.
Heng had never stopped running away prior to A Nightmare in Elm Street. Even though he was training with his heart out, even though he was growing stronger, he never became someone worthy of being trusted. Strength was not the determining factor at this point.