I am not convinced that they are disturbingly predictable. I think in a clinical sense, it is easy to believe so. For example, it is easy to say that children who grow up in an abusive home often end up in abusive relationships, and that sort of thing.
But if you look at a family with a great number of children born one after the other, often it falls apart a little bit. Because the parents are the same, but the children most certainly are not.
I grew up in a family of 8 children. If “parenting” was the only factor, one would thing we would all be disturbingly similar. But that’s not the case at all. We are as different as night and day. And I do mean night and day.
It’s not just what the parent brings to the table, but also the nature and personality of the child, how the child interprets the parent’s actions and the specific needs of each child because those are not the same for any two children. And on top of that, parents are seldom the only adults that interact with children and those relationships factor in, too. There’s an old saying that it takes a village to raise a child. The villagers, so to speak, also have an effect.