Dude how hard are you lowballing peoples marks lol. Can't tell if your still trolling.
I got 98.4, with a HSC english mark of 80 (external exam mark was 84, so I wouldn't call it smashed) - I barely scraped a band 5 for it.
I think you're severely underestimating what you need to get a certain ATAR. Remember that it's a rank, not a mark. So even if someone does "poorly" in an "easy" trial paper, you gotta account for the fact that it's sat by thousands of students across the state, many of whom literally have no idea what they're doing. So while you think a 75% is "bad", keep in mind that there's many students in some noname town in NSW who's class average is probably like 20%. There's also other things like school marking criteria, which could potentially be very strict compared to HSC. Finally, there's also scaling to take into account.
If I only got an ATAR of 85 with those marks, it would mean that you would essentially need to be near top of the school to even think about breaking 90+. Considering that I went to a top 50 school, that would mean that only a few hundred or so people in the state would get 90+, which simply isn't the case. I've got friends who were ranked near the middle, got band 4s and 5s for all their subjects, and still got 85+. You really don't need superb marks and ranks to a reasonable ATAR. Getting 60-70 ATAR requires like band 3's across the board.