Not really.
In my experience (School rank about 15-20ish?), I bludged through year 11, barely studied, ended up topping physics and 2nd in chem and bio. Probably because no one else really cared at that point.
Then Year 12 comes around, everyone actually starts to try, and although it's only half yearlies atm, my ranks fell.
Also, the type of content differs a lot. Especially for chemistry, year 12 exams (at my school anyway) tend to be a lot more wordy with extended response 7mk questions everywhere, because the exams sat are almost twice as long as year 11 exams.
Exception to this is Maths, IMO. If you're naturally good at math it'll carry over to year 12.
tl;dr shit gets real because of competitiveness.