None of the 85% of cultures that preferred polygamy were competitive economically with the dominant Western monogamous cultures over the past couple of centuries.

None, that is, except Islam. Yes, Islam declined over the last few centuries, but how much of it might be attributed to its preference for polygamy, and how much to other factors like, say, Mongolian invasions which barely touched the Western world but destroyed most of the Islamic one twice. Or accidental discovery of Americas

We could posit that building large family networks and having many loyal sons, would be advantageous in those agrarian and somewhat feudal or tribal societies, but would not be beneficial in the modern economy. Perhaps this is why monogamy has been winning and production increasing as a result. Granted these are theories. We write blogs to share our thoughts and impact on others. I don't think your experts should have a monopoly on influence and sharing. Knowledge creation is an accretive, bottom-up process, not a top-down cathedral.

Indeed the Americas have been a huge economic driving force, and especially during the Industrial Age where the USA had a coast on both major oceans the Mississippi River to bisect the Eastern portion and transport cargo most efficiently. And it was arguably the Puritan, monogamous conservative culture (along with a temporary boost of slavery in the South) that drove the great production to harvest that resource.

Again it is all conjecture.