Vayne.
Here is a list of the problems with vayne.
There is no real meaningful counterplay to her. Between tumble and condemn it is nearly impossible to kill her earlygame, which is supposedly how you beat her. You can't stick to her for shit. Okay so then there must be another counterplay right? which would seem to be go HAM on her earlygame. But wait, condemn punishes that as well. So if you farm against her, she wins. And if you try to kill her? you guessed it. she wins again.
3 ad nerf...what a joke. This will have zero effect on her dominance as her flat ad was never the problem, and infact has nothing to do with the problem. I guess if you were to nerf it by 10 or so it might make her have a weaker earlygame, but even then, all she has to do is farm up and make good use of her kit, and she will still perform basically just as well during all stages of the game, with the exception that she wont get kills earlygame.
The fact is that its simply too easy to pick vayne with a safe support and scale harder than your opponent. Its absurd really and reminds me of leesin.
You simply cannot kill her if she is a good player. You got into a good position and pulled off a really good gank? thats okay for vayne because condemn. You are winning lane and about to chase her down for the kill? thats okay because condemn. You are outfarming her? thats okay because she scales harder. You are playing a squishy? she deals probably just as much damage as you, but has a build path that enables her to outsustain you. There is simply no real counterplay to this champion in her current state. Same deal with tristana.
And i know what you are thinking: just pick tristana then! and you are right. tristana can beat vayne lategame. The problem is that this creates a very stale bot lane and if you dont want to play either of those champions you are left with kalista. 3 ad carries that are viable, and the rest are lackluster by comparison. Sure, people have picked sivir in worlds. but none of them have done particularly well due to the fact that you simply cannot kill vayne or trist in lane. Something op about having both a gap closer and a push back.