It's kind of funny, isn't it?
I'm genuinely curious as to why Riot decided to revert the changes to Vayne. It could be from them deciding a different angle could be better for adjusting her, or it could be from the boards and reddit getting in a massive fit over Vayne being buffed. It's like when the Zed changes happened a few patches ago. Zed, being a mid laner who is seen as quite weak in the higher tiers and boasts a 47% win rate, is still viewed as overpowered to the point that he can be near permabanned while having an incredibly terrible win rate. Same goes for Lee Sin, Yasuo, Fizz, and some other champions. Hell, I'm pretty sure if Kalista was ever buffed again a decent portion of the community would rage. And personally as a platinum support main, I find those champions incredibly easy to deal with. And I'm the role who has to deal with assassins the most. Not in lane, but mid game to late game my performance in keeping the assassin away is essentially the deciding factor for most teamfights. Zed's abilities are highly telegraphed as to where he will be as well as easy to predict who he will target (hint: it's one of your carries 99% of the time). Vayne is easily destroyed by Exhaust and any Crowd Control since she's attack speed reliant and squishy. Fizz you space out your CC, using your weaker CC first to bait out his E, then use your hardest CC for when he lands. Lee Sin...well he's just overall weak and I don't know why people cried out when his shield (of all things) got a small late game buff of 80, which at that point in the game is around one auto attack. And I could name ease of counterplay or other frustrating champions as well, but when someone gets outplayed by those kinds of champions then it feels frustrating to the point a majority of players will rush to the conclusion that the champion is simply too strong.
My point is, I think a lot of people need to learn that frustrating =/= overpowered. In all honesty, there are a lot of champions that could use either small buffs or adjustments in some areas to make them better, but if it were to ever happen people would freak out and make those champions permaban. And I think we should stop this way of thinking otherwise certain champions will be forced to remain weak to the point they will never get the adjustments or changes that could honestly make them fairer to play against.