Counterplay to Gnar W passive?

Mini gnar is already meant to kite. I get that. But he punishes melees with his ranged poke, boomerang slow and a hop to get closer/escape. So why does his W have to deal INSANE amounts of magic damage? That scales of % Max Hp. There is no correct way to itemize against Gnar if behind. He can destroy you with his spells and auto attacks. But the fact that you cant counter his W passive is just infuriating, not to mention the speed he gets from it. And while you are struggling to pick up the pieces, Gnar with his massive advantage and teleport and destroy your team.

This is why champions with multiple damage types that are also tanks are just 0 fun to play against. (some of the worst offenders)