3u and 4u takes far less time and dedication than those subjects requiring major works. Anyone normal can do X1 and X2 if they had a tutor, as everyone who does the subject has. I can say personally spending up to 5hours designing, which was about 1/1000 of my folio deserves to be scaled at least the same as X1 and X2. Additionally, constant morning to night graphic work and annotation, updating and maintaining logs and what not and balancing this with an art major and my other subjects, should be awarded more. Maths can cover 4 units, which combined still doesn't equal the work for a 2 unit subject -_-
Whilst I don't do any major work subjects, there are a few things I'd like to point out. At least with major works, you can work on them throughout the whole year, and for some, which consist solely of a major work, namely EE2, once it's done you'll be left with very little to do. I personally think that I didn't put in too much effort towards the yearly exams in year 11, and for MX1 I was ranked 22/185, so I can see where you're coming from. However, I DID complete every last bit of homework my teacher set, and trust me, he sets a lot of homework... What I'm trying to point out is, maths is not a "crammable" subject. You can do it during the holidays and completely disregard it through to exams, and get owned, unlike major works.
On the other hand, from my experience with humanities (I came 1/109 in economics in year 11), they require a LOT more dedicated effort in order to do well, particularly with content rich ones, such as eco and bio. Maths does largely come down to natural ability though; I have had no tutors throughout my life. Basically, in some ways, the scaling system is fair, but in others, it isn't. We just have to put up with it =/
As a quick side note, in my first set of assessments for next year, I did the same amount of work for MX2 as I did MX1. For MX1 I ended up with a rank similar to what I had previously, but after disregarding MX2 for two weeks before the exam and revising the day before, I definitely got below 75%. (We haven't got it back yet, but it was a difficult test =/)