League of Legends (LoL) Question: Is Quinn still a decent ADC?

She can work botlane, but her kit fits solo lanes (and the jungle if you want to) the best. She has self peel with Blinding Assault and Vault, while also having a great roaming tool with Behind Enemy Lines. Her relative low attack range and her weaker scaling compared to other marksmen makes her an unpopular pick botlane, but it can work.
QuinnAD is a high elo Quinn main on youtube who also has some ADC videos of her. You can check him out for more info.

Generally I would say, Quinn is still a decent pick as an ADC. However, she's still kinda outmatched by other marksmans. The reason why she becomes less effective at the botlane is because she's made to be a lane bully (hence why she's so good at top), something that isn't as achievable down at the botlane considering it's a 2v2 lane. Sure, she does have Blinding Assault as a form of self peel together with Vault if she needs a quick escape, but even with that she becomes lackluster in comparison to other ADCs (like Tristana, Caitlyn or Draven for some examples). The only real thing that could make her good in the lane is Behind Enemy Lines as it allows her to roam if needs be, but as an ADC you won't actually get that opportunity all the time and most of the times you're just going to use it to get back to lane. The reason why she's way better for top is because she can bully/zone out her opponent while being able to roam to mid in order to pick up a kill there too.

Overall, she's a decent pick, but is quite outshined by others. Hopefully that helps!

I think she's still decent, or even very good against some matchups, but you have to know how to hold lane to pick her adc. But i think she's pretty decent as she's a crit adc like others adc but if you don't see her it's mostly cuz others adc are better and she's better toplane.