User blog comment:TNickxx/Marksmen, or if you didn't have to follow the meta/@comment-5035765-20160925203741

Corki, Graves, Vayne, and Quinn are played other places because they have certain advantages that make them as good/better in those off-roles

Corki is played mid because he's more of a caster than most ADCs, and has the mobility to get around their tankiness.

Graves has AoE and a pushback on his AAs, as well as weirdly high innate tankiness and somewhat lower gold dependence for a marksman, which makes him good for Jungle.

Vayne has them silver bolts of hers, which eat tanks alive, which makes her good in toplane against all the tanks up there.

And then there's Quinn... for a while she had a different ultimate that switched her out for Valor, who was all melee. This made her ult pretty useless in botlane, since you'd get kited to death (hell, if i remember right, her normal range isn't that long either). Thus, her "meta" positions changed to top (and occasionally Jungle).

So what about everyone else?

Well, that has to do with what meta actually is. Like many people, you seem to think Meta is some arbitrary thing set up by Riot, which is... not right. It's actually developed by the players, for the most part, and is just the optimal way to play said champion. It's not to say that said champ won't work in a position (unless they REALLY don't work in that position, like Jungle Braum or something like that), it's to say "this champ works best here".

With Marksmen, their meta position is in botlane with a support for a few reasons: 1) better dragon control, 2) more predictable ganks (Marksmen are super vulnerable to ganks because they're so squishy and depend on pure damage items), and 3) they get protection from the support, who leaves all the farm in exchange for half the EXP (Marksmen need lots of gold for their builds, which tend to be expensive as all hell)

To add to this, when you put an ADC in a weird position, you're forcing other members of your team to make up for the deficiency you create. Send them mid, and suddenly they have to make up for the missing magic damage somewhere else, or your enemies could do something like build thornmail + Randuins or something and laugh off all your damage. On the other hand, send them top, and your team has to make up for the missing tankiness, which can end up in YOU dying more because you have no one protecting your ass.

So while those champs CAN be played in other positions, they aren't necessarily the best choice for that lane, and can cause the whole team to have to shift around them when they go off-meta. While you advocate for it to be a "just do it whenever you feel like it", you really have to think about it before you do it.