Quinn main here with around 1500~ games on her now.
First step: remove skystrike. It's an overglorified autoattack that restricts Quinn more than it enables. A lot of Skystrike's power budget is invested into its AOE, but that contradicts with Quinn's role as a duelist/splitpusher rather than a teamfighter. Fun fact: Max damage skystrike starts doing less damage than a non-crit harrier after around 300AD. Removing Skystrike will let Valor be used for mobility like intended, and will allow Quinn to receive buffs outside of Tag Team without becoming too oppressive.
Keep her as a solo laner. Quinn will never be a good ADC so long as she has vault, and yet vault is perhaps her most recognisable skill. I honestly think she'll be healthier as a roaming midlaner, but she's also found a strong niche as an anti-melee top laner. I don't mind which lane you choose, as long as it isn't bot lane. Supports punish Quinn far too easily and prevent her from snowballing like she's supposed to as an early-mid game carry.
That said, please give her a way to get into fights that isn't vault. Vault is too risky to use to jump into groups of enemies with, even in Quinn form. Perhaps give her movespeed while walking towards blinded targets or something. Otherwise, really emphasise her trait as a splitpusher/skirmisher if you want to keep her weak as a teamfighter.
Please consider reverting her passive back to 10/3 second cooldown instead of 6/6 seconds. It gives her more of a consistent steroid that rewards you for popping the Vulnerability and provides more counterplay for the opposition. While it's optimal uptime is shorter, enemies can play around it by staying out of range and putting it on a 4 second longer cooldown than otherwise.
Lastly, please buff her vision skills. Her lore depicts her as a demacian scout and yet her scouting capabilities are arguably the weakest compared to her competitors. Compare her W to Kalista's, Ashe's, Nidalee's, Teemo's, etc. Like seriously, Nidalee's bushwhack was effectively Quinn's heightened senses for most intents and purposes but on a 9 second cooldown until it was nerfed recently.
Quinn as it stands is thematically unfulfilling for two reasons. 1) Her weak scouting capabilities as highlighted above. 2) The limitations of Valor as a mobility tool. Right now, Valor is a kamikaze bird, both in Q and R. You can't call Q/V a tag team duo when 99% of the time is spent as only Quinn. Refocusing Tag Team as a mobility skill will increase the uptime of Valor and justify the two's title as a duo.