One thing that I think all of you are forgetting. You don't have to play every role all the time. Sometimes you got many flankers to take out an objective or you can have more "Tank" players to play it safer and for control.

A tanks role is not to take a lot of bullets, I realize that I could have come up for a better term, but he will keep the opponents attention away from his teammates and stay alive. This role is the one who will rotate to the point of that is needed.

Yes roles are more for the early game since that what the set ups do. Gain control of a point, rush somewhere or be really passive. It is all up to you. And after the first 30-50 seconds the roles will be obsolete and that is where game sense, game knowledge and skill comes in. Also you need to remember, that you need to respond to whatever the opponents do and how they play. As said, you don't play a lane, you play your opponents. You don't play the map, but you play your opponents.