In 4e, the Shaman was a primal leader while the Druid was a primal controller. In 5e, classes - especially primary neo-vancian casters - aren't limited to fully handling just one role, so the Druid could easily encompass both leader and controller, and a 'Shaman' could, indeed just be a Druid 'circle' that gets a spirit companion instead of, say, shapeshifting. It wouldn't have to be any more or less leader-ish or controller-y than the other two circles - though keeping some of the leader-y spirit companion functions'd be cool - just more spirited(pi).