So the Marksmen available are: 
But where are 
?
I know Quinn isn't primarily used in the Bot Lane, but if Graves is available why is Quinn being left out? I can't think of a reason why Twitch hasn't been included (if he's too strong for the game-mode, Riot can just nerf him in that particular game-mode).
Probably because how weak Quinn is right now would be made evident.
Quinn is very lacking compared to all of the other marksman. She can be fun to play in the right comps, but she just doesn't offer much. Nearly all of the other marksman outdamage her, while also having more utility and better range. She's not even a better duelist right now since they nerfed her burst significantly and her steroids are sub-par without it.
They need to decide if they want Quinn to be more of a marksman or an assassin. She'll never successfully be both without any hard CC or %hp damage in her kit. If you want an assassin marksman, just pick Vayne, Jhin, or Twitch. If you want a durable fighter marksman pick Graves, Gnar, or Urgot. If you want an annoying scout marksman pick Teemo. Even Kennen is a better ranged top, since he has a far better late game than she does.
There is literally no reason to pick her over any other champion in the game unless you really like her. She needs kit changes to make her more reliable of a pick.
BTW the AP caster Ezreal and the Burst-DPS poke mage AP Lucian are also available in overcharge.
Also, Lucian is just a god in overcharge. First of all, you get him zhonyas, cuz not only does this reduce damage from most other champions there, but you can also just zhonya's when their team catches you while being overcharged, wasting a good 3 seconds of theri time.
Then there's his w, which with AP scaling does amazig damage and is really good at stealing those bots. Finally, his ult is practically impossible to dodge if they're not anywhere close to a dash, and can be used over walls doing tons of damage. Using w and then ulting an overcharged opponent also gets you the hell out of there.
