The probability of fathering 12 children, if anything, is probably inversely proportional to your wealth, these days.
Not sure owning and tending thousands of hectares of land has much utility in and of itself. It was a proxy for generating wealth, like someone owning a lot of equities today. But the question is what utility was available to purchase with that wealth?
Granted kings and emperors in some ways were better off in some ways than the median wage earners today, but not in others.
That king probably had one or more personal doctors, people they more or less owned, whose sole purpose and responsibility was their well-being.
Even if the efficiency of that person might have been low, it's certainly a lot more than being able to rent an hour of a doctors time.
Also, I have a color TV, which no king at that time have, but is that technological progress really wealth?
By that definition, starving people with cellphones are still wealthy.
(Assuming we're talking a couple hundred years ago or longer.)
Who didn't have access to antibiotics, vaccines, or any of a plethora of other modern drugs, germ theory of disease, anesthetics, etc. etc. I'll take an hour of a modern physician's time and access to hospital/pharmacy. Thank you very much.
Quantity doesn't always beat quality.
I even implied as much. What I'm trying to say is that being wealthy has nothing to do with the technological level of your country at some given point in history. It may have some correlation to how good access you have to whatever the highest technology available at your point in history is.
I dunno man, I'm average and can't afford N wives, have someone do my dishes, clothes, own and tend thousands of hectares of land for me, father 12 children.
Maybe i'm reading about different kings than you do.