I think that your kind of experience is enlightening rather than frustrating: it shows that knowing the theory and being able to do the hard questions is only a part of getting the top marks, not the whole thing.
My experience with Methods has given me the belief that those who do the most homework don't neccesarily deserve the top marks. I did every single question in the textbook, made ~150 pages of notes, and ran out of practice exams (~30 full sets of Exam 1 + 2, including all the iTute ones) to do. Looking back now, more than 50% of all that work was unneccesary.
I've concluded that
~ There was no need to go so indepth on notes, a 10-page summary made in a few hours would have sufficed.
~ There was no need to do that many practice exams. I know someone who did ~15 practice exams and got 50.
~ I should have just skipped all the very simple, mindless questions in the textbook. Once you're familiar with doing them, there's no point to doing them anymore. Whether you lose marks on such questions in the final exam depends not on how many of that type of question you have done, but rather your focus and concentration on the day.
It's really hard to identify what study habits are redundant since you're accustomed to doing things that way. Your familiarity with whatever study routines you have will hinder you from perceiving their uselessness.