Quinn's Vault should be a skillshot
It should be a directional dash . And if she hits a target, then she vaults back, deals damage and marks with her passive.
BUT if she misses and doesnt hit a target, then she still dashes, but doesnt vault back, doesn't mark anything, and her movement speed is slowed by 50/45/40/35/30% for 0.5 seconds.
Quinn is no longer a menace to all melee champs, and her enemies have opportunities to counter play against her.