No procreation or power dynamics? Maybe, but that’s one of those very narrow “ifs” that could easily be expanded until it includes power dynamics and procreation which is one of the things that makes it a slippery hill to even step on in the first place.
Family dynamics are twisted up like Christmas lights or earbud wires in the pocket by default.
It does though. Simply being born first, middle or last confers well studied power dynamics.
You can start with Adler, move onto other studies. Children are some of the most “studied” in psychology and there are many families of psychology to go with. Criminal psychology would be a good place to start with incest studies.
Polygamous families, cult families, abusive families all have been picked through with fine toothed combs, albeit biased.
Every family’s a little different and that’s true. It’s not that your hypothetical isn’t possible: I’m sure it is. But blanket advocation may be worse than blanket dismissal.