actually it does affect you.
throughout the year up to and including trials it's good for you to have a stupid class and be comign first.
but in the hsc, you're up against other schools, not just your own class.
this means two things:
1. cos your class held you back you may not have reached your full potential etc.
this is highly debatable and depends on the person.
2. in the actual hsc, the BoS not only considers your individual mark, but also pools marks from your school and divies them back out according to rank and standard deviation.
the mark you get back is a 50-50 combo of these marks.
this allows the BoS to compare schools and rank them, because being first in one school isn't necessarily as good as being first in another.
if your class is dumb, your pooled marks will be lower and whilst you'll still get more marks than anyone else in your class, it might not be as high as if you'd been in another school.
say if there's 10 people in your class and the pool marks are a total of 700, you might get 82 for coming first.
but if the pool of marks was higher, say 850, it'd bring the average up and you'd still have to be first (or close to it) so your mark would now be 90.
best option is to give out notes and help to others after the trials.