A bad player is someone who doesn't know their class' role in a party. If you are a THM that knows how to play well in a party and you know your role in that specific battle, then you are OK. No one has to "carry" a player who knows their role and how to perform optimally in a specific situation.

That being said, if SE cannot balance a class or job's role in a party for certain battles then we have a problem. Either better balancing must take place (I am waiting for 1.21 to pass judgement, jobs will probably help this kind of behavior) OR SE needs to come out and say, "Look, the point of having the ability to be all jobs is that you need to level all jobs because some jobs just won't work for the battles we are creating." AKA "Level a ARC."