So why are we nerfing Vayne again?
Why are we nerfing vayne when there are other ADCs that are better?
Vayne is a high risk high reward chsmpion, but ATM she feels very high risk for a similar reward to most other ADCs that have nowhere near as much risk as her. Vayne has the weakest early game right now (even beatable with ezreal if played correctly) and relies heavily on her support and jungler to carry her through her lane. If her top and jg are 2/9 combined by 20 minutes, there's really nothing she can do as the enemy team will be too tanky (if tanks are fed) or have too much dmg (if carries are fed). Twitch meanwhile can just wait until he gets a runaans and can deal massive AOE damage at a very safe range. If he wants, he can also shove and cheese roam with his stealth around level 7ish. Draven is another high skill high reward chsmpion. What makes him different from Vayne? He actually has a high reward. He can easily snowball and solo carry the game and it's not uncommon for a Draven to be up 5 to 6 k gold by the end of the game. He also doesnt rely on his support or jungler to win his lane. His sheer damage numbers are stupid all game and it's very hard to shut him down especially with the deaths dance build he runs now.
"But once she gets Shiv +IE, she 3 shots you."
This isn't unique to just Vayne. Draven, Twitch, and even Xayah can pull off such damage. Even 6 items, she doesn't compeltely stomp you. Due to her lack of range, she has to get close to the enemy team, and while she may have tumble, she still is closer to the enemy mages, assassin's, and ADC and she gets one shot very easily. She also has no AOE, so a well placed miss fortune ultimate could carry harder than a vayne at 6 items. Plus there's a lot of other things thstcan one shot Vayne faster or as fast. (A fed Zed for example).
"But the changes aren't nerfs, they're buffs to her tank melting power," you say.
Think about all the good ADCs right now. Twitch, Draven, Tristana, Xayah, Sivir... They all build crit. If we nerf vaynes Q crits, she won't be able to keep up with them. The only way Vayne would be able to keep up with crit ADCs is if they made her w numbers strong enough to stack with Rageblade.
"Well what about kog maw, miss fortune, and Kalista. They don't build crit and are still good."
That's because their kits have some kind of compensation that balances them. Kalista deals more damage the more Spears she can put into her enemy. Kog maws numbers with Rageblade are just so strong, he doesn't have to build crit. Miss fortune is a caster, that abuses lethality really well, so she doesn't need crit. Vayne should make up for her lack of damage with her stealth theoretically, but her stealth and mobility isn't very helpful when most tanks and bruisers have lots of cc and gapclosers (Galio, Ornn, Warwick, Kayn, Camille), plus they deal quite a lot of damage relatively until 5 or 6 items.
Speaking of tanks, they have high base damage and lots of natural resistances. Champions like Skarner, Kled, and Renekton only have to build 1 or 2 damage items and then full defense and not only can they kill you in 1 rotation of their abilities, they also end up tanking the most damage. Back in season 5, tanks would take damage, and not deal so much damage. They actually did what their name says they should do.
The W "buff" also is a nerf. Late game she does less percent true damage and less minimum true damage. What about the early game true damage? 10 to 15 true damage won't make a difference. This isn't nearly enough to outweigh the W percent dmg nerfs much less the q nerfs. Plus her Q gives her so much mobility in lane, and more stealth. Not maxing it leaves it at a 5 second cooldown until late mid game which is actually quite long.
"What about the R buffs?"
Well they aren't bad, but it encourages a more Master Yi kind of dueling playstyle that isn't suitable for ADCs (meaning she would become some kind of top laner). Maybe if they increased the AD on it, it would feel better.
TL;DR: Vayne is a high risk high reward champion that is getting her crits nerfed while Twitch and Draven deal similar amounts of damage with WAY more benefits. Her early game is the worst of any ADC right now and she relies heavily on her support.
