Ergo, whatever environmental influences shape personality come from outside the home, not inside.

How far apart were the different homes - in the same neighborhood? School district? I also wonder how different the parenting styles considered were; at the same economic level in the same town, for example, divisions in "style" might be minor compared to people elsewhere, of different means.

It doesn't seem plausible, but you assert the books have mountains of evidence and I am not curious enough to check myself, so I ultimately withhold judgment.