As I said before though, Quinn's got a lot of raw early game power--contrary to the archetypal hyper-carry who relies on the accumulation of items to get themselves going (or in the case of Nasus and Veigar, on stacks)--and is very vulnerable to being shut down late game due to the nature of her kit (low AA range, two melee-oriented abilities central to her damage output, general non-tankiness). Even if I build her with late-game damage in mind, I'm not going to be doing too much of it if I keep myself from using my two most potent steroids during a team fight, and I'm definitely not going to have the safety of other hyper-carries like Jinx (who has insane AoE crits), Vayne (who has Stealth and two potent modes of self-peel [Quinn has one in the form of Vault, but once she's engaged in combat, Tag Team provides little in the way of an escape]), Kog'Maw (tons of range), etc. I could sit there and AA everyone to death, saving Vault and Tag Team only to chase fleeing prey after a teamfight, but how can I be guaranteed I will survive until that point if there is nothing stopping the enemy ADC from dishing out my damage and more from further away (getting in range of the frontline oftentimes means getting in range of the hyper-carries, which leaves Quinn vulnerable to them--and she can't get to the hyper-carries without facing the frontline, so she's screwed either way--good luck trying to poke with your Q!). The point I'm trying to make here is that hyper-carries are designed with the purpose in mind to carry games through their insane amounts of damage as well as safety by which to dish it out.
Sure, Quinn's a decent assassin, but she's got no reliable escape once she's eliminated her target (unlike safer assassins such as Zed and LeBlanc). Assassinating enemies as Quinn relies on them being spread out, uncoordinated, and/or poor decision-makers (your ADC should not hang out towards the front of your group if there is an assassin on the enemy team). And sure, she's a good duelist, but she has little in the ways of keeping herself alive as soon as she engages 1v1--enemy teammates are sure to follow up and make quick work of her in a late game grouped-up scenario. She's just more difficult to teamfight with and less safe than other Champions in general. All these things point her out as a non-hyper-carry, at least not by what seems to be the traditional sense of the word.