What is the deal with Vayne?

What is says on the tin really. How did Vayne get through beta testing without someone noticing just how OP she is? There is no art or skill to playing her, just run head long at the enemy and hope not to get into an early team fight.

The only time she's realistically killable is early game, once she's got a Blade of the Ruin King, that's it. Pack up and go home. I've seen so many games going equal till the twenty minute mark, only to then be broken by Vayne. You can throw whole teams at her, and they come back in pieces.

It's ridiculous. You can't out tank that kind of damage, you can't fight it either due to how much life steal can be stacked. It just gets worse and worse. You either throw everyone at her and hope that one person comes back out again, or deal with the rest of the team, and then get picked off by her.

I can't be the only person who's noticed this. So I ask again, why, oh why, hasn't something been done about this?

I know that perfectly balancing all characters is impossible, some will always be better than others, but this is taking the mick.