The most annoying part about vayne is not her true damage
It's the fact you can't fucking escape from her. You can be playing singed with rylais and ghost and she will just ride your ass while running and gunning and you can't do shit about it. You're just fucked.
And also the fact that she's so hard to assassinate. You better hope you have enough burst, or enough burst and CC to erase her before she can react. Or else her point and click condemn+roll will just end up with you being counterassassinated.
In actual well coordinated teams? Sure, she can be shut down easy. But in blind pick/randoms/yoloqueue, she's a nightmare because not only do you need the right team comp to deal with her, but you need to have actual teamwork, and that doesn't fucking exist.
So most of the time you are just fucked right at the start just because you don't have enough hard CC/burst to deal with her.