Vayne is not "OP", arguably she is weak in pro play. Often when I lane against Vayne I win the lane, often very hard, she falls behind like 60 cs or so and dies multiple times.
Vayne is problematic however because this is not enough, I can not in any way what-so-ever stop her from snowballing. I had a game where I went vs Vayne toplane, I was winning and zoning so hard Vayne only had 36 cs at 18 minutes and had died 4 times, I had 4 plates down. We both recall and Vayne at this point however decided to go mid, and somehow gets a double there in no time when my jungler and mid tries to tower-dive. She recalls and comes back top, and she just press R, and pretty much 3 shoots me now.
Vayne is just too forgiving, and even if she falls hard behind she just need like one lucky fight and she is right back and outscaling everyone, despite being like 80-120 cs and 1-2 items behind. Champs like nasus at least will suck if they don't get farm for the first 20 minutes, most other adcs will as well. Most ADC's depend on being ahead or at least on pair with everyone in farm and items or they become super weak. But Vayne is fine being massively behind.
Vayne is due to her comebacky nature a massive issue in none pro play. In Pro play you have a team of professionals that are on the same page and want to end asap. In solo Q you don't have this. You have a team running around and chasing kills.
Sadly Vayne for some reason has to be designed with pro play in mind and therefor riot allows for Vayne to be annoying in other ELO's. Yet for champs like Teemo a different philosophy is applied and Teemo have been gutted for long due to being so annoying in low ELO. Nobody talks about balancing Teemo around pro plays. If they were Teemo would need some massive buffs.
Vaynes kit is also an issue that makes me hate facing her.
Vaynes kit gives has something to deal with everything, the only thing that matters is usually how Vayne is playing, not how I'm playing. If you play a hard engage champ, she can push you away, go invisible, tumble away etc, and probably 3 shoot you. The only way you get her is if she screws up. Vayne got an easy time itemising vs anything too, let's say you play a poke hero, she soon has life steal with runes + items and your poke no longer matter. She can just eat it and heal up from 3-4 autos on minions.
Vayne is just never a bad pick, she is good vs tanks, squishy champs, poke champs, none poke champs etc. While most other champs are situational. But what I hate most is that there is no way of shutting this late game carry down. The "conter play" is winning pre 20 min, this basically requires that all your lanes are winning, but say mid + top is loosing, good luck "winning pre 20" from botlane.