I have actually come up with another theory - English is there to stop STEM students (Hear me out).
A lot of stem subjects have a lot of crossover in the sort of skills they need (i.e. physics needs math, engineering needs physics, so on). These skills are usually characterised by problem-solving and understanding the concepts presented to you (Very broad stroke). Many students have these skills from birth, and they can uniquely be better taught to students from a young age.
If we were to ditch english, these students would much better be able to run wild in the courses - the STEM subjects with higher scaling means that they can just dedicate their life to those skills. While that is not necessarily a bad thing, it does mean they line themselves for an entirely STEM job. This should be their choice.
The issue comes when you have students who do not necessarily have those same skills. They will pick subjects like Business studies or history or languages or something not STEM related, which may be hard, but does not necessarily scale well. (This looks at a deep rooted issue in our education system.) So, students could theoretically do a bunch of subjects that have such easily transferable skills (Not just something as general as essay writing, since essay writing in economics is very different to essay writing in history) and do brilliantly, which then makes our nation move to more STEM-based qualification.
While this may not be bad, there still needs to be some variation in the sorts of things students do, and other students need a chance. Enter English. English is aimed (Since it must count to your HSC) to stop this entrenchment - it works virtually the exact opposite way to any STEM subject for some unique reasons:
1) Extremely subjective - other than spelling and grammar, everything is subjective, nothing is objective
2) The ways you support your answer must be backed up by evidence that is not necessarily obvious, as in a thesis in economics could be supported with facts, but a thesis in english must be supported by analysis of a piece you must do yourself (I mean you can look it up but still)
3) Everything can be argued - that is, when you enter an exam, as long as you back up a claim with evidence, anything is right. This not only forces children to think critically about what exactly their opinion is but investigate why it is so.
4) Really, English is an art (especially writing creatives). You could do all the analysis into different eras and writing styles, create the perfect formula for a piece, but in the end, it is an art. You need to be able to naturally replicate a piece by taking conventions and integrating them with yourself.
5) Math especially has a process - this does this, which leads to this, which leads to this. You cross a threshold where you can completely understand what is put in front of you. With English, you need to constantly learn and absorb information, and you never truly know if you are ready. Also, you need to be much more adaptable (With new syllabus change) to the situation at hand - while math problems require problem-solving skills, answering an English question needs you to formulate a response of what is an opinion, and you never really know when you have finished supporting it.
While we all would love english to be gotten rid of, would we really appreciate having to compete with students who have had tutoring since they were 3 years old in math and who now are Gods at it? Personally, I don't think my daily visits to Khan Academy could ever go toe-to-toe with tens of thousands of dollars of tutoring from a young age. I by no means support English - but I can see a reason for having it.
Please debate - I am keen for feedback