If you really want to balance both champions in this game!
You first need to change the matchmaking. Right now the system tries really hard to get you to a 50% win rate or close to it. This is unfair since you get matched with though enemies and weaker allies. If you play well eventually you will loose because of "some strings" being pulled by the system. This means your statistics are irrelevant since you can loose a game even if you are 10 - 0 - X so if a champion has a powerful kit no matter how well he does matchmaking will destroy any meaningful data.
Find a matchmaking system that is rewarding instead of punishing you for doing well.