It can be a real complicated mess, can't it?
Who should determine what's best? What judgment of what is best for that child in that family and that set of circumstances can the system provide and what does it have to leave up to the parents, fallible as all parents are in their own way? Even if the system "can" provide judgment, should it? These are big, fundamental questions that go far beyond money and to the heart of the relationship between the State and the family.
It really is a mess. I had no idea how very unfair (and seemingly unconstitutional at times) it can be until I got involved with someone who has kids from a previous marriage. I know I'm biased about his case, but before he and I were involved even as friends, I knew some of the details and I still thought it was a crazy mess.
One thing is guaranteed in any family court proceeding: Someone, somewhere, is going to get the shaft. And unfortunately, that usually if not always ends up being the child.
I'm not a fan of the current family law system, and yet it's still infinitely better than the way things had been addressed in previous incarnations. There really isn't one answer, to any of the questions. It has to be a case by case determination. But OTOH there is a limit to the resources available to look at every detail individually and there have to be rules that apply to everybody. Those rules must preserve the constitutional parental rights of both parents as well as (hopefully) take into consideration the best interest of the child.
It's not an easy situation, even just taken at the court level. Now expand it to something like the benefits described in the OP, apply the larger constitutional framework of due process and equal protection and you can see just how ridiculous it is. Obviously the person proposing it has no real knowledge of the issues, the constitutional elements involved or how the system in general works. And who'll end up getting the shaft? Once again, the child.