Just to add on from the perspective of a law student. I think that getting 80%+ in individual law units is definitely possible, especially if they are first year units (they are slightly easier imo and you get more resources like PASS). However, some people do better in later years because the way you study for law doesn’t really change much, and once you have a process down, it’s easier to do well. The difficulty in law is trying to maintain that 80+ law average throughout your degree. Like Sine said, the average marks in law are pretty similar to other courses, but they’re more bunched up. From what I’ve seen it means that unlike other courses there aren’t a bunch of people getting averages in the 90s and even in some individual units, I think the highest marks have in the past been in the high 80s. Basically, 80+ average is possible but difficult.
As for commerce, it’s definitely easier to get higher marks in commerce, but there are people who get higher law marks than commerce due to complacency and lack of interest in commerce units (basically what Sine said).
Also, people don’t always have those ATARs in law cause a decent chunk of the cohort are transfers. Not that ATARs really mean anything in university anyway.