Elementary and middle school are even less like being an adult than high school
I think GP's point is that the school environment is nothing like "adulting," so your original point was just plain wrong.
And I agree with the GP: I don't see any reason why home-schooled kids would be at a disadvantage to public school kids when learning to navigate the adult world, because the school environment is strange and not at all focused on "adult life skills."
It actually made for a very unsafe college experience. I had no experience telling anyone no, or doubting anyone's intentions. It took being lured alone with a man to realize that he didn't want to study Calc I, he wanted to make sexual advances on me when I was alone. I was lucky to learn that lesson without getting sexually assaulted.
Took me another few years to realize that I didn't have to obey everything my boss said, even if it was personally detrimental to my career.
My mom, of course, would tell you how great it was that I wasn't socialized with "an unnatural collection of same aged peers" and how I was always "so polite around adults."
Hmm... so you're saying that students aren't segregated into artificial cohorts of a specific age, and there isn't an authority figure in the classroom telling them what to do?
Perhaps that's the case where you live (though I'm...skeptical), but it certainly is the case here and everywhere else I've ever lived.
IIRC that sounds a bit like Montessori (done right), but that's uncommon generally and extremely uncommon in upper grades.
I wasn't even sure what an upper-grade Montessori program would look like, and I found this: https://amshq.org/About-Montessori/Inside-the-Montessori-Cla....
This is not an accurate description of school. Maybe, maybe in high school and college you kinda sorta get to something resembling that, but for elementary school and middle school it is nothing at all like your description.
I'll grant you that 40-50 years ago it was a bit more regimented. I'm old too. But I have school age kids in both elementary and middle school, and I have a lot of experience in what their environment looks like. It's very dynamic, lots of hands-on learning opportunities.