Sorry to hear you had a bad homeschooling experience and you disagree with the data with regards to success rates (there are roughly 3.7 million children being homeschooled currently in the US). It works for many, I’m sure there are folks it might not (you mentioned some sort of cult situation in your case;
I don’t believe this is typical except perhaps if you consider religious reasons for homeschooling).
The average person with no training in teaching or education isn't going to do better than the average person with said training.
Your stats aren't all that meaningful for the following reasons. What percent of homeschooled kids meet the criteria for "structured homeschooling"? Without this information it's not a meaningful stat.
There is also selection bias going on. They tested reading, writing, arithmetic. Did they test algebra? Did they test biology? I'll bet a fair number would fail at questions regarding evolution or have a skewed view of historical facts.