Everyone forgot why Vayne is popular right now.
Vayne has pretty much been the same for a long while and has never been a major problem. She is very good at counter engaging due to the nature of her kit.
She was not played much when sustain/utility supports such Sona, Nami, Morgana and Soraka were in season due to the fact that she has no poke, very like harass potential and could easily be harassed. Now with all these, Threshs, Leonas, Alistars, and Braums running around, of course she's gonna thrive and dominate.