Not the wall behind me.
Very easy to avoid this.
Not the area beside me.
Don't fight her up close in the river.
No, an auto-attack doesn't count.
She's an assassin.
Yes it does. There are a lot of assassins who can devastate with autos. Yasuo, Master Yi, Talon (less now than in the past), Garen, Sejuani, Vi, Fizz... I'm not sure why you think assassins don't have any use for autos, ever.
She's supposed to be high skill cap.
She is. That doesn't have to mean she's not low skill floor. The concepts of skill ceiling and skill floor aren't joined at the hip. Like Master Yi, she's pretty easy to do okay with, but to truly shine with her, you need practice and a little talent.
If she whiffs her Q, her E, and her ult, and only manages to land an auto after hitting her W, she shouldn't be blowing me up.
But she does.
Tank, mage, assassin, support, doesn't matter.
This one, you can blame on the meta. She's not the only champion that does that right now, by any stretch.
She can miss her ult entirely (or not even aim it at you) and hit a wall to chunk you for half your HP.
Avoid walls around Qiyana. It's very possible.
No other assassin (besides maybe Katarina, headbutt R collect LP) is able to just miss everything and still get a kill.
Yi doesn't even have to land anything. He doesn't have a single skillshot. Ahri can miss every single R and still get kills if her AP is high enough. Kha'zix doesn't need to land E or even W to get kills, he just needs to land his targeted Q's and autos. There are other assassins that behave this way.
In general... Qiyana is a risky melee assassin with minimal range. If you burn your mobility getting in, you may find it hard to get out if things don't go the way you planned. Conversely, it's hard to get in position for your combo without using E or W to close the distance. Qiyana requires decisions, and if you make the wrong choices in the moment, she has no defense. Her health and resistances tend to be extremely low. Without mobility or her water Q, what is she to do when she makes a mistake and jumps into two high-damage enemies? Sometimes even one will do.
Qiyana's fine. Not perfect, but fine.