Just like one could live their life wholly not applying the same level of effort you describe here to their lives, living on “zero learned skill” and purely “instinctual means” alone.
I’d argue having children is the same. You can do it with zero effort, or you can do it with intention, to leave behind a better off generation, and devoting yourself selflessly as a parent to that cause.
I believe the lifelong quest of high-quality intention is what ultimately is the greatest achievement of life one can chase. Whether that is intentionally treating others with kindness and leaving pleasant memories, or intentionally raising healthy and inspired children who will continue to take up noble intention.
Penultimate means “second to last”. But what is your message, that children are the most precious heritage or not?
I would argue that those who leave the most behind are those who are kind and thoughtful to those in their lives. They leave behind one of the most important and precious things that anyone ever could - pleasant memories in the minds and experiences of others. They brought direct happiness to others through their kindness. This is the type of person I strive to be, and I feel enriched and deeply fulfilled when successful in doing so. In some ways, the type of peace that can bring can be one of the few things that you can "take with you" in death, in that you will feel that happiness until your very last moment, which you will most likely not generally do with material possessions.