How to position as vayne?

I really don't understand at all why people think vayne is op. Even when I get fed I just get instagibbed by a flash insert nonskillshot move. IMO she seems completely trash, ALL of the other close range adcs have a way of doing damage from farther back, except vayne. QSS does nothing if you instantly die. Basically the only way I can survive teamfights is to just sit in the back line doing nothing until most people have died (which is usually mostly on my team because we have basically no adc), and then I have to flash away from someone that will inevitably jump on me and basically instaburst me. All they need to do is drop a single pink ward and vayne has absolutely nothing going for her. Seems to me like she is purely for when the enemy team has no dive whatsoever, or if you are playing against garbage players. You are pretty much forced to get a QSS and a banshees if you want to have any chance at doing anything, and even then you still just die from pure damage. I keep trying to play her simply because she is really fun and does have an insane amount of damage potential. Still, someone like a jinx or tristana sits back completely fine and does barely less damage while being infinitely safer.