I don't know anything about you "Inside Out", so I don't want to come off as sounding presumptuous.
I get the distinct impression you haven't experienced any form of disadvantage. It's like you're saying, "Well, it shouldn't be that hard to get X ATAR, despite experiencing this and that".
I'll just say this, to an extent you really have to experience being disadvantaged, in order to understand it. So, for instance, attending a terrible school. It's easy for people to say, "You can just work hard at any school and things will come your way". It isn't as simple as that. Try attending a school where you're being persecuted for your race, and yes that does happen in schools. Try attending a subject where the teacher has been partying with your peers the night before and hence, doesn't give a rats arse about teaching the class in general but, instead, wants to socialise with their "friends" i.e your peers. Try learning in an environment where disruptions are the norm, where discipline isn't actively enforced. This isn't even applicable to all "terrible" schools. Not all schools can be categorically defined by these "norms". Some exhibit it, some don't.
And that's just one "factor" that people can experience. How about an abusive family environment? Or an underlining medical condition ? Or this and that .... (I can't list everything at the top of my head)
But what I am trying to say is, I think you're generalising too much. Oh, and I know someone who got an ATAR of 84~ and topped a few of his units last year, at UoM. So I really doubt there is, to an extent, a correlation between ATAR and Uni grade.
Also, I'd say the SEAS system isn't perfect. Sure, people abuse it and I know a few people myself who did but, at the end of the day, it does help those few who do need it. It's honestly better than nothing.