How are tanks even supposed to remotely itemize against her? Is this considered balanced?
Vayne has always had %max HP true damage, and as far as I can remember it's always been 8% at max rank. It's something Riot's defended on several occasions, and there nerfs to her kit have hit everything else besides it when they've needed to address her.
The bulk of Vayne's damage is physical auto-attack based due in large part to her ult's steroid and Tumble's bonus damage as well, which 
all hit with a double-whammy.
As for her true damage, consider:
A) LoL is a game reliant on skill and using tactics and stratagy to a certain extent
B) No tactic or stratagy works 100% of the time in LoL
You can't dodge point-click skills with mobility.
You can't land point-click skills on opponents in fog of war, stealth, brush, invisibility, stasis, or untargetability.
You can't use Tenacity or Cleanse vs. slowing fields, knockbacks, pulls, suppression, or knockups.
You can't damage invulnerable targets or targets that refuse to drop below 1 hp.
You can't rely on out-tanking someone that's tankier than you.
You can't rely on out-running someone that's speedier than you.
You can't rely on out-ranging someone with more range than you.
The answer to every champion simply isn't just counter-build them even if you are a tank or fighter capable of doing so.
With Vayne counter-building her will force close to 37.5 AAs with her %max HP ture damage alone though.
This is in a game where Nasus can 2-shot a squishy, so it's not like counter-building her damage does nothing. You just don't get to be invulnerable vs. her if she manages to hit you 30+ times, and she gets to do something if she manages to survive within 550 range of you long enough.
In regards to fighters - getting within striking distance of her as a tanky DPS like Nasus, Shyvana, Warwick, Olaf, or Udyr and flat out killing Vayne is your stratagy. Difficult if you telegraph your movements and get immobilized by the enemy team. Not particularly difficult if you use walls, brush, fog of war, and/or wards to approach her from a difficult angle and land a few hits. She's a solid chaser, not a great runner.
In regards to tanks - Vayne is the highest priority target on the enemy team to lock down with CC. Her front-loaded burst is pretty low and her damage contribution will rapidly climb the longer she's allowed to auto-attack, which most CC prevents her from doing. Vayne's defensive mechanic is mostly reliant on out-maneuvering her foes as well, which CC generally stops.
In most cases true CC tanks counter Vayne much harder than she counters them, seeing as most are amazing at initiating a team-fight and locking down priority targets, where Vayne is a mediocre team-fighter by most accounts and does not handle being locked down very well.
Anyways - don't assume defense is always the answer. In regards to a lot of bruisers and fighter/tanks it's pretty useless as well, darn hybridized physical/magical/auto-attack/ability damage output.
But every champion has different strengths and weaknesses. Your job is to find them out, exploit their weaknesses, and avoid their strengths. Not try to muscle your way past their strengths with your weaknesses.
physical damage.
Isn't physical LOL and by the way, a tanky fighter and an hyper carry ADC are completely different champions. Balancing is completely different as well. Be more salty that frozen heart isn't going to save you. You don't pick single target pick champions against a vayne she's one of if not THE best duelist in the game. Zed, Xin zhao, Rengar, etc. that shit dosen't work against a good vayne. You need AOE. She has short range so if you force her to hit a frontline that isnt trying to balls to the wall dive her alone, then your AP and maybe even your support will have the room to kill her without even focusing her. But you're probably one of those kids who just tunnel visions the vayne with no pink ward or bckup CC or anything. gets outplayed, and cries that she's broken.
