.............. welllllllllll..................
c: EDIT: In seriousness- she's obviously my favorite carry and I feel like I win a lot of the games I play with her (granted the losses are very painful when they do happen). Personally I feel she's very... hm, "active"? Aside from her W, she can very effectively use all of her skills in comparison to, say, Caitlyn, who barely needs to do anything but auto attack in fights.
this is someone I know irl; I'd like to think he's done pretty well for himself, and as you can see he's in gold IV with Quinn as his most played champion, so I wouldn't say you can't use her if you really wanted to (as I have been). The blind and ability to very quickly proc her passive twice (and potentially crit both times!) makes her a pretty good duelist, and with her ult's attack and movement speed, I always find it very easy to surprise someone splitpushing somewhere and blow them up relatively quickly. Whenever I'm playing Quinn I never give up regardless of how the game is going because I know if worse comes to worse, I can just try to catch people alone later on when I have my core build and explode them. I also know a friend of Ame's has played her as an AD assassin mid, which is also perfectly acceptable because of her ult's roaming ability and execution damage. I've also played her top with a more bruiser-y build (including, say, trinity force and sometimes frozen mallet for maximum kite) but those games ended before late so I couldn't really tell just how effective (or ineffective) it would have been eventually.