No one cares about ATAR at uni. It's a rank / snapshot of 1-2 years of your life. Australian
Tertiary Admissions Rank. Bolded the 2nd and 3rd words on purpose. I have done two degrees at two different unis and it has actually never come up once - in terms of comparing etc.
Also if my HSC is dissapointing but got offered a position in any of my preference then I will use my post-hsc holidays to prep for first year uni and hopefully I could get that 90+ WAM in first year.
This is a good idea. Stick with it.
Note that all you need is to actually get into a course and then you can transfer based on 1st sem/1st year grades. Even if you didn't get into uni at all, there's still bridging courses to get in that wouldn't require you to repeat Year 12 at school.
I strongly recommend you don't take that path of repeating year 12. There are so many pathways these days to get into a desired course. Not getting into your first pref is not the end of the world, which is what a lot of people think.
ATAR is not an indicator of success at uni either. I am a perfect example of this. I got ~65 as my ATAR but ended up with WAMs in the upper 70s in both my Bachelor and Masters, with several 90+ grades. I won't lie, it is
extremely difficult to obtain a 90+ WAM in a uni degree, whatever discipline it is. Given most unit grades are weighted (in the sense that multiple assessment tasks/exams contribute to it), you'd have to be pretty bloody consistent.
we're expected to keep our WAM above 70 which is probably equivalent to turning up for classes and handing in assignments etc but not really putting in extra effort
Eh... I personally disagree with this statement. It's not easy to maintain a WAM of 70+. For some it might be, but for the vast majority, it isn't.
tl;dr don't repeat yr 12, you can still get to where you want to go. ATAR is a tertiary admissions rank and that's it. Don't let it define you.