Originally Posted by NotBuzzJack
Also I feel you've never heard of Silver Bolts.
I have heard of Silver Bolts and frankly I'd argue that that is a bad ability as well. Anything that takes up a button should have a reason to press that button or it should not be there. If there's no reason to press the button the skill takes up you're actively reducing the amount of play involved in the character. That said, Silver Bolts does not make Vayne completely useless if you turn it off. Because Vayne is a ranged ADC and every piece of her kit is built around auto attacking she's still strong, if a little under powered without silver bolts, but no worse than any other ADC when they're low on mana.
If you play Vi and turn off her Denting Blows however she becomes utterly useless. Unlike Vayne who's whole kit revolves around her auto attacks Vi's kit is disjointed and awkward. Her ult is a single target CC, her Q is a telegraphed skill shot making it easy to dodge, her passive is a shield that activates off skills on a cool down that makes it difficult to predict, her E is the only thing that on paper pairs well with auto attacks but using it makes her attacks feel even clunkier than they already are.
Vi is an interesting character, I was very excited for her when I saw the splash, and read her lore. She's easily one of my favorite characters thematically, but her kit is a complete mess that makes her not fun to play.