Voli has 1 damage ability, falls off late game, and is easily countered by many commonly played champions.
Just because he can face roll Bronzies that can't hit the lane with their skill shot does not mean he is OP.
I mean sure, when you are over extended in your lane, don't use any wards, and the most reliable team mate you have is a caster minion....he can certainly be scary, but who is really at fault there ya know?
I have been plying Voli since his release and in ranked hold a 60% win rate with him over multiple seasons, he is no stronger now than he ever was. His power comes from back picks and bad play, he is next to worthless once you get into gold or higher unless you are just a boss.
What are you going to nerf on him?
His Passive has already been nerfed....
His W has already been nerfed and only really deals a lot of damage to someone who is already dead....
His Fear only effects minions......the slow is short.....
What do you want to nerf, his W? Then he has nothing.....
Long story short, learn to play a champ with some CC.