You have stated the position clearly, but I've never agreed with this theory.

First, we don't at this point know how long the affection between Mr. Bennet and his wife, and the happy-family period, lasted, but it would have had to last several years for it to have influenced both Jane and Lizzy -- Lizzy is younger, and so even for it to have lasted until she was five years old, it would have had to last seven or eight years. I seriously doubt that it lasted even that long -- surely within a year, if not sooner, Mr. Bennet would have recognized the stupidity of the woman he had married -- but perhaps in future weeks, there will be evidence that we can discuss and return to the subject.

Second, it was not customary for Regency fathers to have much hands-on involvement with the raising of their young children. Of course, that doesn't mean an individual father might not have. In fact, I can see Mr. Bennet recognizing that Lizzy's sense of humor was similar to his own, and so he would have interacted more with her once he reached an age where they could banter, thus honing her sense of humor, but he doesn't strike me as the sort of father who would have enjoyed young children. It may be, though, that the sense that she was loved by her father influenced her, even if he influenced her in no other way.

And third, one major way that Lizzy and Jane differ from their sisters is in their sense of propriety, and it seems unlikely that they got that from Mr. Bennet.