imo vayne is better if you can get some real good peelers, especially against kassawin.
ali is one, rammus is another.

an early grez can go a long way to avoid getting juked or to bushwack and +20 armor against bruisers (not much but at least it's better than +0).

perhaps you can try flash instead of cleanse and get scimitar if you need the cleanse so badly.
flash is just real good for squishies atm.

I'm definitely not #1 Vayne NA, but I've never really had much trouble 1v1ing Xin as Vayne. I haven't played pure dominion in a while (catch the teemo too stronk), but her kit seems ideal for destroying Xin. Other champs always gave me much more trouble.

I'm not highe Elo by any stretch, but I've usually found Trinity Force + The Lightbringer to be a decent build on her. Tri Force gives you some extra damage up-front and a decent sampling of AD, AS, Crit, and some MS and Slows for better kiting potential - which Vayne is reasonably good at, considering she can both knock back enemies and gap-close forward herself. Also, Dominion is over to fast to really get much out of going one Auto-attack attribute at a time, IE+PD builds tend to work in Summoner's Rift because you already have both scaling each other when things get interesting - so I like getting multiple scalers right away. Zeal and Phage offer a mini IE+PD interaction of AD, AS, and Crit - plus having some extra health to survive 100%->0% comboes is nice. Having the movement speed to outrun the generally faster melee champions can come in handy as well.

Vayne has a gap closer and Knocback herself though, which allows her to get some pretty good distance, and prevent most champions with gap closers from sticking to her that long. Only real problem with gap closers against her is if you can't tumble and/or Condemn someone directly after they use one on you - so if Xin is smart enough to save his third talon strike, you're going to have a bad time. If you can manage to Condemn Xin into a wall when Final Hour is available, he's toast - but being reasonably solid with landing 3-talon strike is a lot easier than lining up a stunning condemn.

I lied. I'm actually a high elo player who used to main Vayne. I know how she works and while what you and said aren't incorrect, there exists multiple speed shrines in dominion which make her almost useless. You basically have to play her as if you have 10 hp, avoiding all things when you dont have your front line in front of you.
That being said, a vayne in dominion should be building PD/Shiv, iedge/sang (depending on their team comp), LW, a defense item. PD + iedge is usually my core

Is this sarcasm ? anyone with a gap closer is hell for a champion with Tumble, condemn and Stealth tumble in ult form ?

We should get Duelpower in here. He's probably the best Vayne I've seen in Dominion.

Hate to beat a dead horse but xin amongst others make Vayne have a bad time.
You get only -1- shot at winning a duel against xin, that is if you hang by a wall and wait for him to E to you, tumble away from said wall and condemn him into it.

You miss any part of that and Xin gets another notch on his headboard.

If you have a mallet though, xin does absolutely nothing to Vayne. You condemn immediately after his charge, don't even have to stun, and he dies before he can touch you again if it's a 1v1. The real problem is the rest of his team diving you if any bit of cc touches you.

Why would you spend that much money on Frozen Mallet? If you want the slow, just get a phage and keep it, maybe turning it into a Triforce if you get fed enough to have a full build. That much money could be spent elsewhere getting more pew pew.
You're also assuming that the Xin is an idiot.

The mallet guarantees that basically whenever you see *anyone* 1v1, you can kill them, with no possible escaping from them, while taking next to no damage after lifesteal. After you have two offensive items in PD and Sanguine/IE a defensive item in FM imo is a much better buy than another offensive item.
You kill things fast enough already, and more survivability/being able to easily 1v1s things like jax, xin, kz is worth more than your diminishing returns on damage at this point as your final item.