Can someone explain why Vayne is so bad now? Is it because of the E nerf?
The meta focuses on stronger, more aggressive supports, which makes Vayne 's early game even more of a problem. Her low range means she can't safely farm without taking an Annie stun, Karma ultimate, or Leona shield to the face.
The nerf only solidified her has unable to win trades in lane. Her main combo in lane was AA, AA, condemn, and the third AA proc from the condemn. Removing this crippled Vayne 's ability to win trades (harrass).
Thirdly, she's simply out classed. Her late game steroid (bolts) is hella strong against tanks, but a well-itemize Tristana or Jinx will do more damage even to tanks, due to their steroids. A 90%/115% ASP steroid is stronger than silver bolts.
And, lastly, the meta is pushing out the ADCs who are weak midgame, including Caitlyn and Trist. These carries offer little objective control compared with the Big 3 (Jinx, Lucian, Sivir) and crucial objectives are often lost between 17 and 25 minutes.
In short:
Want strong laning? Catlyn, sivir, lucian
Want a good seige? Caitlyn, sivir
Want a strong overall transition between lane and midgame? Jinx, lucian
Want a good late game steroid? Jinx, trist
The enemy has TWO or more HP stacking champs? Vayne
An honorable mention here is Varus, who lost favor due to his lack of an escape. Stronger supports let Varus remain as aggressive as he should be during the entire game, and he also has a % HP shred.