I just don't understand Qiyana at all conceptually.
I'm not talking about Qiyana jungle obviously because there you completely trivialize what's her biggest weakness, which is surviving laning phase.

So level 1 you have to let the opponent push, you want to farm your first wave under turret.
Which means you'll get poked and denied some cs from harrassment.
Then you get level 2-3, where she gets her strongest powerspike and should normally destroy anyone in lane, but if you suffered too much poke while trying not to get denied 2 entire waves you can't really outstat the statcheck, even with her massive damage, unless you play against a squishy no damage early mage, and there are a few, but take for example viktor which shields himself from level 1, or zoe who can bubble you mid combo, what do you do if you can't somehow get your cheesy kill during this powerspike?
What if the opponent just play safe on that powerspike and you can't get a free kill on them during it?
Then you get to 6, which is a very powerful spike but a more coinflippy one, as a mage goes from being a sack of gold to actually having kill potential on you.

And then, as the game progresses, you get outscaled by everyone.
Bruisers, tanks, fighters, juggernauts, mages, adcs, even enchanters stack so much heal and shield power they can deny your burst.

And then you get to midgame where mages can safely annihilate their waves and you cannot roam anymore without losing plates and being even more behind.
Because playing assassins, but qiyana in particular, is accepting that you will play from behind, always, unless you get turbo fed. It's like starting the biggest race of North America but your legs are crippled. You clearly don't get the best odds.
But if you play a mage, you don't have to sweat early too much, you can poke safely, you just know you'll linearly scale endlessly and eventually you can oneshot anything. Why would anyone pick qiqi mid?