PSA for those who are looking to use Vayne:

First, figure out why she's powerful. She's good because now she's actually quite versatile, and can become a monster lategame. Her versatility comes from how you choose to reach that late game. PtA, Fleet Footwork, and HoB all bring different options to the table.

HoB makes Vayne an early game champion with an actual late game, but is quite unnoticeable once you actually reach the late game.

PtA makes Vayne an all-around decent champion with a good duelist late game. I recommend using this if you have a healing support. This is the rune that will generally have the most impact late-game in duels, while still compensating Vayne's early game.

Fleet Footwork makes Vayne good in the sense that it strengthens your early game survivability, but not so much your prolonged duels. It's good for quickie trades, but mostly is used as a band-aid for healing, when Taste of Blood and Ravenous Hunter just aren't enough, such as against Lucian, Draven, poke supports... etc.

Lethal Tempo with the crit rework approaches meme-tier levels because with newer picks like Caitlyn rising back to prominence, and with Lucian STILL being quite powerful, your early game isn't compensated enough by Vayne's lategame, and using a full second of stealth will cut into your tempo time. HoB is better early game, and while Lethal Tempo IS noticeable late game, it doesn't synergize well with her kit, and you will feel a lot of time wasted.

Another big factor to her versatility is the combination of Taste of Blood and Ravenous Hunter providing a lot of natural sustain thanks to Vayne's W and Q. With these, Fleet Footwork has no longer become THE necessary keystone to take, but can still be used to provide a lot of healing.

Second, realize that Vayne will not outscale traditional crit ADCs anymore, especially Tristana and Jinx. Champions with a built in attack steroid WILL out-trade Vayne's W and R stealth. Vayne will not be able to compete with them through traditional tactics, so it's best to play Vayne as a duelist in those scenarios rather than a true ADC. Her stealth will still do wonders, especially with the Q buff, but you have to be smart about it.

Third, remember that Vayne can be played as a safe ADC. Especially with Fleet Footwork, Vayne can easily trade small amounts over a long time if necessary. This will of course drastically cut down her damage output, and if you want to play her like this as your primary play style, I recommend Caitlyn due to her longer range and longer dash range.

In teamfights, this approach works too. Wait for someone to get cc'd, combo with a cc into the wall while autoattacking, and it'll usually result in a kill unless they're a really bulky tank.

TL;DR: Her versatility comes from how you reach late game, her "outscale potential" has faltered in the face of Tristana and Jinx and co. and she can be played in a safer manner. It's not necessary to be Gosu every single time someone glances at you.