There might be a way to fix Vayne...
So, Vayne has been quite popular on the boards as late, only to be surpassed by the rage fire Nidalee caused some months ago. I would not know of another champ that has caused so many complaints over such a long time.
The problem with Vayne is not really her access to hard cc or the %-Max HP damage - those only feel more unfair in combination with something else: the low risk combined with the high reward with this champion. Sure, the damage type is a problem too but the Fiora rework has proven that this mechanic CAN work - if you have to earn it through skillful gameplay.
But what do I mean with low risk? I'm not refering to that she has a safe lane phase or can deal better with being ganked than other adcs can - but her fighting pattern itself is the problem, making her also annoying to deal with at toplane. There is never any reason you would use your Q TOWARDS your opponent during a fight (unless you already won and they try to bail out). There is not one good scenario for this, so ofc no one does this. Instead she stays at range, where it's much safer obviously, but without paying anything for that safety.
But we don't need to nerf her safety for that... but we could add some risk to the kit, an ability that would ENCOURAGE getting close and personal with the enemy.
You have a similiar thing with Xerath's passive: Usually that dude would NEVER even come close to the enemy laner. Way too dangerous when you can shoot lasers from safe distance (see pre rework xerath) . But on the other hand now there is this sweet, sweet double mana for basic attacking champs...
We need a similiar greed-inducing ability that could become the new W (and moving silver bolts to where it belongs: the passive slot). I'm thinking about something like: "Next basic attack is melee, triggers and applies silver bolts, bonus damage when hitting the enemy from behind. Will also apply bonus damage from tumble as that one is triggered "on the next attack after the roll")
So insted of a
roll away -> push you away -> throw basic attacks from safety -> repeat and use E when needed
you would have
Shoot two basics -> stealth-tumble past them -> melee attack from behind -> Finish the job with E to get them away from you or get greedy and try to hit two more basics and then your E (as long it's not on cooldown)
The old play pattern would be still possible with this, but less rewarding. And the other would be rewarding, but you just used your tumble then and if condemmn fails or is on CD you are kind of screwed. The reward comes with a risk after all ^^
Of course for this to work I propose two more changes to the kit.
One affecting her silver bolts: they will deal PHYSICAL % damage, but when the last shot is made by an ability the damage turns into % health-TRUE damage. As I said before, the damage type is fine, as long it's not given away for free.
Another change is to give her a new, actually interesting ultimate and move the stealth to the tumble (stealth duration on the levels being 0/0,5/1/1,5/2 or something like that. Zero on the first or maybe even the first two levels. Rough numbers, don't bother too much with them please). The new ultimate should be something better and more interactive than just a stat buff. Might even be something more utility focussed as she would get a new damage spell with the W. I could see her using a smoke bomb or another "gadget" (she's Valoran-Batman after all...).
It would also fit her theme a bit as her weaponary does not really allow "rapid fire" (see Lucian/Miss Fortune/Twitch maybe) or "big shot" (see Ashe/Jinx/Cait/Tristana/Draven/Ezreal/ and some others) as a good theme without being kind of weird. With the new W she would already have enoug damage, so some combat utility (I'm still thinking of a vision-blocking smoke bomb here) might be the way to go.
Sure, this might make her even stronger, but harder and riskier to play, so that's fine I guess. And the frustration naver came from Vayne being too strong actually, but from her being untouchable in teamfights while shooting from range and therefore winning by default THAT'S what pisses people off...