The point is historically--and across the animal kingdom--the default is parents minimally "prioritising relationships and resources on a parent to child level." Irrespective of odds of survival.

> fallacy you've fallen into from your prior post is to confuse that population level dynamic with the parents drive to pass on their particular genes

The drive to pass on genes is biological. It operates at the individual and group levels. We have no evidence the desire to pass on one's genes has any biological roots; reckless abandon produces more offspring, after all, and plenty of species, including humans, show both kin preference and out-of-group sympathies.

> insane to me that it isn't even possible to consider the parent has an instinct to prioritize relationships and resources with children most likely to reproduce

We're having a discussion. It's being considered. The problem is the evidence is stacked against it. If a phenotype is conserved across animals and humans, the simplest hypothesis is it has utility. At that point, evolutionary pressure at all levels will tend to work to conserve it. Including through parental instincts.

> some want to work hard to make sure it isn't seen as a reasonable hypothesis

It's a reasonable hypothesis. The problem is it has no evidence for it and plenty for the null. Pigs roll over and smother their piglets. That isn't a sign of hidden selection pressure, it's just bad parenting.

That said, I'm not cleanly rejecting it. We don't yet have a good model for the genetic basis of mental disorders. And a lot of mental disorders, e.g. a tendency towards random violence, could have served someone well in antiquity. So it very well could be that parents rejecting kids who won't have children in high school is innate to some. But again, we have no evidence for it.