Hey sotirod
member of the MHS class of 2016 here, btw.
And I can say that I went through similar circumstances to you a few years ago. I came from a low-quality school in year 8, where I consistently topped my class in maths tests without trying, and I didn't give schooling much thought because of sporting aspirations - at the time, I didn't even know that MHS existed.
(tangential anecdote here: I didn't prepare for the select-entry exam until a couple of weeks prior to it - my mum gave me a few maths MCQs and I didn't even know why I was doing them, I just did them for the sake of it. At the select-entry exam, I had no idea what I was doing there, I just answered the questions to the best of my ability without knowing the end reward. Then when my mum found out I got into MHS, she woke me up in excitement, and I was still lying in bed thinking
huhhhh... Eventually I figured out the magnitude of the result.)
Then when I got into MHS, I went from possibly top-of-the-year-level in my old school to the bottom half in terms of academic ability. My average in maths tests slipped from over 100% (because of bonus marks in my old school) to around 70% in Year 9 Sem 1 to around 60% in Year 9 Sem 2. In English I was in the bottom third of my class for sure. And Science as well, literally couldn't give a damn back then - due to an increased focus on my sporting aspirations. Plus I almost failed the Year 9 Sem 2 History exam. Looking back, I can safely say that I simply did not try anywhere near hard enough at the time, to hold my own against my peers. I'll blame all the iPad games for that year-long mishap.
This poverty of work ethic continued until the middle of Year 11, when I ceased my sporting commitments (due to factors that I will not mention). My 3/4 was Business Management, and I was at the bottom of my class by a long shot - everyone was averaging A/A+, and there I was with a filthy C average. But I threw the kitchen sink at my studies for my last three semesters at the school, and convincingly made it into BCom at UniMelb when my ATAR should have been something below 90 if I kept up the level of work ethic that I had previously.
Being at MHS for 4 years, and UniMelb for 2 years, I have learnt a lot about my peers and institutions:
First, I can whole-heartedly agree with you about the "fabricated and hidden b---s---". Our median ATAR is slipping, and our median study score dropped from 37 to 36, while numerous other schools have shown improvements in their scores; something does need to change in MHS for sure.
Second, academic success in Year 9 and 10 (i.e. the academic merit badges that people walk around with on their blazers) is only weakly linked with VCE success. Some who were in the top 10% in Year 9 have fallen from grace, whereas some who have not received academic merit have gone on to achieve 98+ ATARS, myself included. To add to that, VCE success is not linked with uni success. Some with convincing 99+ ATARs have not made Dean's List (top 3%) in their degree, while others with ATARs below 99 have reached another level.
Now for some advice. Definitely stay at MHS. The sports, extracurriculars, and prestige here is not available in any other high school for a male student (except maybe Nossal and Suzanne Cory, I'll leave that debate for others to engage in). For all its discrepancies, I still feel proud of being an MHS alumni every day, and I will for the rest of my life. In addition, the scaling of assessment grades is beyond belief, mainly due to the cohort as a whole doing exceptionally well on the GAT (my C average in Unit 3 Business Management scaled up to a B+, and my B average in Unit 4 English scaled up to an A+). Just getting into the school puts a hefty premium on one's ATAR - an 80 in a below-average school can become a convincing 90+ at MHS (sure, people complain about the teaching staff every day, but they're better than most in the state).
It's great that you're engaging deeply in sports and extra-curriculars. When you get to VCE, I recommend using the school gym on a regular basis. Definitely helped a ton with my stress management and confidence building.
You also said that your commute to MHS is 2 hours one-way (that's harsh...). The best advice I can give here is to start assignments as soon as you get them instead of procrastinating. In VCE, there will be no assignments (for most subjects); instead, the primary form of assessment will be in-class tests, which I prefer compared to research assignments (typical of geography & history). I feel that it is easier to prepare for a test than grind out a research assignment.
And lastly, MHS may mask things with their "prestigious status", but why not leverage that to your advantage? You'll be a catch at whichever uni you attend in the future (Mr Slocombe's words, not mine; he said something along those lines at the Year 12 final assembly).
Hope that helps, and I hope you find conviction in the decision that you make. All the best for your secondary schooling.