Blackstone's exposition of the common law of England says, "They (the children) are by law HIS children".
By converting them into HER children, we force assignment of care, custody, and protection into the hands of the party who is (almost) always least prepared to carry out those responsibilities.
We then seek payment as punishment from the exiled father, as if he were a class enemy like a kulak in the ukraine under Stalin.
Not only are children in the custody of single mothers more likely to fail, thousands and thousands of them are murdered, battered, or sexually abused by the psychopathic boyfriends their mothers bring into their lives.
The entire system is an unsupportable mess which is generating the criminals of tomorrow - and this case is merely the tip of the iceberg.
You are correct. The standards for custody obviously changed. The real problem is that the standard "best interests of the child" is not a standard at all, but a justification for doing whatever the hell the courts want to do.
Moreover, the old standard "the tender years doctrine" is actually still being used, they just lie about it. Sad really.
What I meant by the common law when I referred to it earlier with regard to the default standard, I meant the current common law, not Blackstone's time periods.