40 mins is a long time to write, don't you also get 5-10 min of reading time in HSC as well? plan out your response during reading time and just don't stop writing for more than like 30s.
if you're using a memorised essay, sure, maybe you can write without pausing. but you're not actually even sitting the exam at that point or engaging with the question, you're using 40 mins to rewrite something you memorised. if you have general format or scaffold memorised, fine, but you could achieve that just by having written enough for it to be muscle memory how to write an introduction and structure sentences.
i think what a lot of students are missing, by nature of how school works, and one of the unequivocal advantages of tutoring, is practicing writing an essay under exam conditions and getting proper feedback on it. realistically, you only write like maybe 1 or 2 essays a year in the leadup to senior years, then come y11 and 12 you write like maybe 6-7 tops? there aren't many skills where you can practice once every few months and actually reproduce technique with muscle memory to a level of competence. if you have enough practice, there's very little time difference between writing your own essay and a memorised one, if anything, writing your own essay is easier because once you have the hang of it, you don't really need to stop at all except to occasionally cross-reference your introduction and ensure you haven't strayed off.