SpaceCadetThis order drastically changes when you factor in what division or skill level you are talking about IMO. I think the class most in question is Medic as he can easily carry more at lower levels than at higher levels. His direct impact on the game has a higher potential at lower/mid levels and therefore carry more for the team.
At lower skill levels, a really good medic can mitigate mostly all the mistakes those type of teams make by just being in the right position or being able to read a fight AKA game-sense. I'm not saying this isn't done at the highest levels but the medic typically isn't the class who is making that happen in those cases.
At lower levels this is definitely true, having a medic who's in the right position and survives can singlehandedly win rounds even if the rest of the team is worse (e.g., I rang for a friend's main team and the other team forced me to medic and despite every player on our team being heavily outdamaged and having more deaths than their whole team we still managed to win two rounds because I micro'd everyone and survived: http://logs.tf/2607314#76561198059645150).
yightcombo scout > demo > flank scout/roamer map dependent > pocket > med (carry potential)
med > combo scout > demo > flank scout/roamer map dependent > pocket (baseline potential)
Not sure what 'baseline potential' means exactly but I will agree that in close matches medics' performances are some of the most important because it's so easy to drop players or drop uber or get caught out and lose rounds, but I would say that corresponds to the fact that medic is very easy to fuck up on. Not playing poorly does help your team but I wouldn't even say that's really carrying, if both medics are playing well it doesn't really make sense to say they are both carrying. And if one medic messes up and has a bad game and the other doesn't, it seems more fair to say the one who played poorly was holding their team back than the other medic particularly carrying.
That said, if your medic has crazy mechanics and simply doesn't die to bombers and has crazy surfs and stuff that would definitely count as carrying in my book. Strictly speaking, medic definitely has a huge skill ceiling and there is room to play optimally and never get caught out and have perfect games and arrow the enemy med and stuff like that, but I'm not sure how that compares to the carry abilities of other classes. It feels like on medic even if you are having your best game ever there simply isn't *that* much you can do so long as the other medic is playing decently, your teammates kind of have to step up and actually kill stuff even if you constantly give them uber ad pushes.