I don't know if this is a math problem, so I'm just gonna drop the objectivity... There are some teachers around here, so they'll have better answers to this...

But in my opinion, teachers should both consider the individual capabilities of a student and the capabilities of the entire class, as they can't make individual exams for everyone. In this way it has a positive outcome for the not-so-well scoring students and the good-scoring-students. But using this curve has a negative outcome for the pupils who are in the middle...

Though I think it's rather hard if not impossible to find a good and balanced method for everyone

Not sure, what you want me to answer, just gave my 10 cents