Hey there,
You've already filled the first criteria to History Revolutions and that's having a keen interest in wanting to learn history.
I was not in the same position as yourself, I had completed both Units 1&2 before 3&4, however I had achieved C's throughout Units 1&2 year and it drove me insane, because I genuinely understood the content, it was the structure of my writing that let me down the most- the same dilemma that you're hypothesising about.
However, I managed to turn it around and began to obtain high A's in Units 3&4. What truly helped me was reading the VCAA Student Reports- they are your holy bible for Revs. I strongly recommend reading the exemplary pieces on the Reports for the 5 and 10 markers, because they give you a good indication as to what the examiners view as an exceptional structure response. There are also good notes on the Atar Notes website that may help you out.
Remember that the structure for writing in Revs isn't as complicated as some would have you believe and what I found out. Remember to always give your opinion on the prompt- you can never be neutral on an issue- and always signpost as it makes it a whole lot easier for teachers and examiners to read and understand your ideas and thoughts on the question that you're responding to.
Hope this helps and good luck with your academic endeavours.