If you want to nerf leblanc REVERT her R back to damage amplification!
I remember they changed Leblanc R to deal 30% increase damage of the mimic spell. Back then she has clear weakness!
if she wanted to push and more mobility she would max W, if she wanted more damage she would max Q.
She had clear weakness >:3. Even with silence she could not push a lane and she was way more balanced.