But this also means either (1) being homeschooled was also good for you academically, or (2) the school system up to secondary school was terrible for people academically.

I don't think you give quite enough credit to the possibility that, in fact, what worked for you academically was pretty close to what you got: an early introduction to the basics, lots of free time to explore what interested you, and then getting formal schooling more on your own terms.

You may indeed have thrived from a younger age at school, but also maybe not if you'd gotten a string of bad teachers and unpleasant classroom dynamics when you had less capacity to handle it. Or you may have enjoyed it more and done okay, but actually ended up less creative and less confident--fine, and happy at being fine, but missing something. Or you may have done better yet. It's hard to know.

It's not hard to know, however, that what actually happened educationally worked quite decently.

Your case for it not working well for your siblings is stronger. The outcome simply wasn't very good, so there's a lot more room for potential improvement.