I feel like Riot can't decide if they want Quinn to be an assassin, an ADC, or a diver. Her current design seems to go in all three directions without being particularly good in any of them. I personally don't think she'll ever work as an ADC or an assassin, not with their current design philosophy about meaningful counterplay and whatnot. This leads to her being binary as all hell, because if she's not bursting someone instantly there's no point in picking her over someone else with more safety and in-combat mobility/mitigation/utility. Her kit would be perfect as a diver, if she had a bit more CC, but that probably wouldn't be in line with her character or lore.
On top of all this, most players don't particularly enjoy playing with or against Quinn. Look forward to her getting more changes in the future, until Riot figures out what they actually want her to be.