Just a tit bit about roles, Some are hybrid others are supplementary

In case anyone didn't notice most roles in league are supplementary, while others are hybrid. what that means is that champions are one role with some elements of another role. Yi for instants is a skirmisher but has aspects of being a diver, as his Q is a diving ability as he does in balls deep to hit multiply targets. others like Vi and Lee sin are divers that hit nearly as hard as assassins while still having a shield. then we got the oddballs like Gangplank and rumble are melee battle mages(GP being more of a skirmisher ) that are rather hard to classify while Singed is just troll(actually juggernaut/battle mage but let's be fair he is one)

Either way I hope this clarifies things on the subject on primary and secondary roles.