Child B. Child B without a shadow of a doubt.
You do not know this, and you have absolutely no data to back this up. It is not possible for that blanket statement to be true.
There is no one solution that works for everyone. Many kids excel in public school, and many kids struggle with it. Many kids are much better off avoiding the public school system. I know I struggled with it quite a bit and spent more time avoiding people who were trying to beat me up because I was different (didn't listen to Poison and Ratt and didn't spell psyche "S-I-K-E") than I did learning anything. However, I know many intelligent people in my class who did well in public school. Although I feel I would have been better off without it, there is no way for me to know for sure.
My wife and I choose to home school my son because we found that by the time he was going to be attending first grade, he was already way ahead of where most of the other children were going to be in his class. He is currently 9 years old, and we get evaluated every year by a qualified, certified teacher. If we get to the point where he is falling behind other kids his age, we will reevaluate our plan. In the mean time, we have joined a local homeschooling group, and unlike in a public school, he gets to hang out with some kids his age, some kids older, and some kids younger (more like real life in the adult world), and learn to get along with people without the pressure of having to be ashamed if his own tastes may be different from the tastes of others. He gets plenty of socialization, and gets to hang around older kids who are great role models of how to be in charge of your own learning. I know 2 kids, one 15 years old and one 16 years old, who are homeschooled but are taking college classes to supplement where they have exceeded their parents' ability to teach more complex subjects. Neither is having culture shock due to lack of social skills. Neither is floundering because they can't acclimate to a classroom environment. They excel, and I believe that it is because they are bright kids and they feel that they are in charge of their own destiny. They do not sit around waiting for someone to teach them.
Just because you can imagine how something could fail doesn't mean it always or even often will. Just because you had a particular experience and turned out okay doesn't mean that everyone else should have that experience, too. There are plenty of parents who use the guise of unschooling as an excuse to not discipline their children. There are also just as many parents who use the public school system as a free baby-sitter so they can disengage from being active in their child's life. To dismiss a form of education because it can be abused is short-sighted at best.
... I could not know all that I do today without those mind-numbingly painful drills and lessons and test and reviews.
You don't know this, either. It may make you feel better to believe it, and that's fine for you, but all you've convinced me of is that you don't like to distinguish between fact and opinion.