Yeah I agree. If you just rote learn the basics 50% is very achievable and will scale to a 77-80ish HSC mark which is roughly a 97.5-98 atar contribution. From my experience Advanced requires almost perfection to do really really well, whereas Extension 2 is just more content but in comparison to advanced does not require near the same amount of perfection as advanced does.
In a way if you are already half decent at math extension 2 gives you breathing room. I know a friend who missed a lot of school towards the end due to sickness and never properly learnt mechanics, so he didn't bother studying it at all and got 0 on every question in the hsc but still got a hsc mark of 80.