I have mained Quinn as an ADC since her release and would like to think I have had really good success with it (even with her never technically in the meta). I see her discussed and played primarily as a top or mid lane pick though but my personal preference for her overall is as an ADC. Now I am biased towards this because I main ADC in general as well (I haven't experimented as much with her in mid or top). As an ADC for her, I try to rely on her huge burst potential. Almost no other ADC is able to fight her 1v1 IF she lands her q. Even though I love playing Quinn, I fully recognize her issues as a reliable ADC. Many of these have been mentioned already but the top three for me are as follow:
- Her passive is on a timer which makes it unreliable
- Her Q is make or break in duels. It almost guarantees a winning trade against the other ADC or other AA based champs if landed but seriously hampers your potential to win if you miss. Also, by late game the opponent my pick up a qss which renders the blind useless.
- She is a poor ADC for teamfights.
The biggest one for me is the third one though. Based on her ult, you make her a melee champion which really defeats the purpose for having her be your ranged ADC. As a result, I tend to treat her more as an assassin. I use my ult to flank around to instantly burst their ADC before a fight breaks out if possible. For competitive play however, this is almost impossible. Being able to have your ADC flank without being caught and escape shouldn't ever happen due to more vision around the map. So this means that she is more likely to be in the back line for an actual teamfight. Here is where I believe she struggles the most. Unless you have bork, you don't have a good means of taking out the front line as some of the other ADCs.
Split pushing works really well for her but then I would agree that she would be better suited for top because you still would prefer to have your bot ADC to be with the rest of your team. If Riot really wants her to be an ADC then her ult definitely needs to be reworked because its just not suited for an ADC during a teamfight. I personally feel like she is still missing something though. Whether that gravitates her more towards top lane or bot lane, I don't know but I feel like something needs to change for her.
Feel free to disagree with me on what I have said. I personally have had success with her in both normal and ranked so far but she is one of the only ADCs that I play completely differently. I'm curious as to what others have to say with response to my post though.