I agree. I went to private school for a year and did well. I went to public school after that because private was too expensive to maintain, and it was not so good. A few non-burned out teachers who made a difference, mostly just soul-crushing apathy and stockhold syndrome all around. And I would love to have learned to program and read earlier, I am not sure how I managed to go that long without reading, I guess I was just different developmentally.
This is very much a to each their own thing. It worked well for you but it also sounds like you had a uniquely active family and community to support this. The primary problem with homeschooling and unschooling is the lack of family support. Either by apathy or by lack of economic opportunity. Or simply their own lack of education preventing them from even being aware of these options (such as finding a community to coordinate with to make up for their on educational deficiencies).
I can't speak for all public schools, my parents deliberately chose better than average schools for my sister and I to attend. But good public schools exist. Good teachers exist. But just like good home schooling and unschooling experiences, this requires either luck of birth (well-to-do parents) or deliberate effort by parents to improve their children's position.