I got 35% in my Year 11 yearly last year my rank was 16/37, not a bad one but it's just so many works and I didn't understand it at all.
True, General's scaling is crap, but if you intend to go to uni then general is better than no maths. The good thing with General is you can spread out your time for other subjects as well which in the end, you may get a better marks across all subjects. I've done ok in the last 4 terms in general and getting 80%+ is not impossible. My trial mark was 82%, trial rank: 1/51, final rank: 1/51. I highly doubt I would get the same if I'm still doing 2 units maths.
Depends on what you want to do in Uni, courses such as Maths, engineer do expect you to study 2 Units maths but others such as Science, Computer Science and lots more courses don't require that, General Maths is perfectly fine
Don't worry about the scaling. If you do badly in a subject, even with the best scaling ever, you will still get a very low mark. However if you do very good in a subject, even with the worst scaling ever, you will still get a very high mark. Do the subject you like and you will get a good mark but not based on the scaling.
Hope this helps and good luck with your study in your HSC.