It's amazing what taking only part of a quote out of context can do.
Meddler-
TLDR: It's possible Vayne's too strong, so we're looking at her. 'Everyone says' doesn't necessarily equal true though.
There are a lot of anti Vayne threads on Boards, with you there. That indicates that, at the very least, a lot of players are finding Vayne really frustrating. Frustrating doesn't necessarily mean overpowered however, though the two are correlated. Champions sometimes generate a lot of frustration feedback even when balanced or underpowered (e.g. Blitzcrank really annoys some people regardless of his balance state and waves of anti Blitz threads crop up every so often). It's also important to remember that the population of Boards isn't necessarily representative of the entire player base (it's a subset of the english speaking population from certain servers).
Having said that though it's very possible Vayne's too strong at the moment. Her win rate in solo queue is quite high for such a popular champion. That, particularly when combined with the frustration she's causing, means she's worth investigating. Doesn't necessarily mean nerfing Vanye's the appropriate outcome though. It's possible we might find that Vayne's too dominant at present because the champions that should be keeping her in check in lane are weak and need to be buffed. Or because items she scales especially well with are overpowered. Or because other meta conditions (lots of HP stacking champs for example) are very favourable to her. Or even some combination of all those factors and too strong a kit, hence the need for some investigation.