No.
It does not matter what school you go to. You can still quite easily get 90+. There's always quite a few people in my school that get in the 80s range, and always a few that get 90+. My school is also one that's ranked fairly low in that list.
Just make sure you're ranking first in sacs. The boosting your ATAR score thing isn't really that true, but being in a strong cohort will mean that you can afford to be lower in the sac rankings (as stronger cohorts mean sacs would probably get scaled up).
The school that you're at shouldn't really disadvantage you - to get a good score you'd be needing to put in your full effort anyway, regardless of where you are at.
In response to what giveup said, incidentally, most of the teachers at my school are actually pretty damn good, despite the low ranking of the school. Every school will have their share of good teachers and bad teachers (looking at this forum, I've seen a few MHS teachers be complained about - even though MHS is one of the high ranking schools in Victoria). Resources - not so much (mainly talking about trial exams), but you can source them from elsewhere.
Hard working cohort is something you might miss out on, and it's a non-issue really. It might even be an advantage, since it'd be easier to maintain rank 1.