In this case, don't make his growth go "skyrocket" in speed. Instead develop his skills, as he has the advantage if the system. Make "world energy" a reason for people to keep fighting. The stronger beasts they fight, the more one will grow; yet even then it would take centuries to overthrow the old order.
One may have the skill, but lack in strength. Yet if one has strength, but no skill, then they will be nothing but another pawn. Strength and ability, the difference is the amount of time required to grow those attributes.