I would have to say that parental neglect made three of the Walls children stronger in the long run, the exception being the youngest daughter, who does not appear to thrive in adulthood. It is difficult to say to what degree Maureen's position as the baby in the family accounts for this different outcome, too.
The Walls children were forced by parental neglect to rely on their own inner resources, in effect, parenting themselves and often parenting the parents as well. To what degree their environment created strong adult personalities and to what degree genetic traits enabled this outcome is impossible to say. And this book is by no means a model for how to raise a family. The parents, while they had their own reasons for their flaws, were really monsters of selfishness, creating chaos and pain in the lives of their children, who managed to survive into adulthood against terrible odds. The stability and success of three of the children was achieved at great cost, and the kind of childhood they endured more usually results in more pain, adult dysfunction, and an inability to parent a new generation properly.