I don't think it's a myth so much as it really doesn't reflect the broad range of both possible and actual home schooling scenarios.

When home schooling is used as one aspect of minimizing broader social contact for your children, it can be an issue. But it's not the home schooling per se that is the problem, but the attempt to narrow their world. And I agree it's totally unfair to paint every home schooled child with that particular brush.

But they do exist, and where they exist, most would highly benefit from traditional schools if for no other reason than it breaks the bubble a bit.

Having know a bunch of people who were home schooled in various ways I think your claim of clear superiority of preparation for adult life is also a bit too strong. On the whole I'd say it's a bit of a wash.