in pugs
both scouts > demo > both soldiers > medic
in high level league play
pocket scout > demo > flank scout > pocket soldier > roamer > medic
here I'm interpreting carry as "if you have a pop off game your team will probably win". over the course of many games I'd rate the importance of individual performance of each player in this order
pocket scout > demo > medic > pocket soldier > flank classes
imo the combo is by far the most important part of any team