Whether he wins or loses, he's still a fucking godawful miserable experience to see in a game. I would rather deal with any of the most-banned top laner juggernauts right now than Lee Sin.
The issues are manifold. Consider this recent experience:
I'm Teemo minding my own business, shrooming a retreat path deep in the safety of our Blue-side jungle. Our jungler, Sion, heads toward dragon through river. Then Sion goes flying from river to raptor camp, bumping me at the end of his movement. Sion's still perfectly healthy, and I'm dead. 1-shot. 80% to 0% with around 1200 damage.
It's easy to understand why it's miserable to be safely minding your own business well behind the front line only to be literally deleted by a single skill from a champion you never saw, who was not in range to attack you, while you were positioned safely and correctly.
Beyond that, it's just generally unfun to play against champs that can't be peeled and can't be chased, can dive but are anti-dive, and can take advantage of fog/vision while leaving you tagged with true sight. Unless the Lee Sin is a mouth-breathing fucktard or it's super late game, you never ever feel like you have a fair chance against Lee Sin.
Again, it's not whether you actually win against him or not. It's that 100% of fights involving Lee Sin feel like he's a dirty-fighting cheater. It's that every fight with Lee Sin feels like the outcome is based on his decisions, not yours. It's that every time you kill Lee Sin 1v1, you know that he could have escaped if he wanted to. It's that his kit has the vast majority of things everyone hates seeing when they face Riven.
Also, his sound effects are the most annoying thing in the entire game. I would rather listen to Lux and Blitz spam laugh for 45 minutes. Lee Sin sounds like he's straining to push out a constipated stool to the point of hemorrhoids.
