A lot of the time Teams that work/play together a lot tend to learn how each person works in a situation or with a weapon/power, and how best to deploy themselves based on the other members...that said, sometimes you do need some to grab a group by the scruff and shove them into the place they belong. With a game as open as this is going to be deciding something like this before hand, or on the fly requires a lot of understand of the people you're with. More often than not, natural leaders arise and find themselves leading their team to victory, or defeat. All that said and in mind, I personally would recommend a semi-rigid rank structure for things like planning, and griping, for the team in the field, let them figure it out how they want it