So when did some of the kids fulfill their class roles?

When Dave fought Jack he exploited the flow of Time as a weapon by using many time copies. When Rose charted a course to the new session she was using her Seer abilities to guide them on a most fortunate path. When Jade was grimbark she was a very active fighting presence using Space as a weapon. When John used his retcon powers he was acting as powerful carefree influence on the narrative.