It's okay Riot, we all make mistakes. Who would've guessed that turning Vayne into a more unfair version of Akali is fundamentally broken and makes her the best ADC in the game? Surely it was impossible to have the foresight to know this.
Seriously though, of all the potential ways to buff Vayne, they had to do it in the most annoying way possible? Being infinitely kited by a champion you can barely see or attack is unfun. The ult buff on its own guarantees that Vayne outduels anybody that can't immediately 100 to 0 her.