(1)
You can't just compare ancient empires with modern liberal economies.

"Proven capable of having a civilization" /= "capable of creating and maintaining a free and open society".

Egypt was controlled by a Greek family for centuries. Before that it was some weird death cult in the hands of all powerful god-kings.

IQ is less of an issue in pre-industrial times where people were expected to do as they're commanded, economies are top-down and rigid, retribution is swift and final and most people are either farmers or salves. These systems are designed to deal with low IQs - like every human the low IQs are going to be obedient under threat of immediate brutality.

Just because a few managed to keep the masses under strict control, build up armies to conquer,and the upper crust of society produced some art and poetry, doesn't mean that those peoples can transition into a meritocratic, innovative, democratic, free economy. And in a world where different types of societies exist, the meritocratic higher IQ ones will outcompete the others, and the low IQ ones will be dysfunctional unless lorded over by an iron hand.

Of course the low IQ will grow more resentful in a society where they're constantly bottom, than in some ancient world where everyone more or less were subsisting on the same misery.

(2)

As far as I know, IQ correlates less with negative characteristics in populations with a lower average IQ. That is, while a white person with an IQ of 75 will be emotionally stunted as well, a black person will not be (at least not necessarily).

I don't intuitively believe this. I'd have to see some sources. It makes no sense. They may be from different races, but they're not a different species. And in the context of low IQ populations of the US this is just blatantly false, those correlations I mentioned are just as relevant for low IQ as everyone else.

(3)

IQ is highly heritable in developed Western countries, because all the environmental 'efficiencies' have already been reaped.

IQ is highly heritable everywhere, but you are right that heritability is not the only thing that affects IQ, and poverty factors in particular can have an outsize effect. As long as the average IQ is low the prospects for a functional society are low too, but of course if the average IQ rises then those prospects improve.

China went from an average IQ of around 80 to over 100 in record time, as their economy improved and things like malnurishment declined. But the Chinese people in western nations were already above 100. So a better indication of the potential for IQ in populations is the IQ of their people in western countries. Some populations have stagnated around 85. I suspect we only know this because it's so shockingly extremely low that it was impossible to hide. You probably won't be able to find any further breakdown of other races. Couple that with the reality that the IQ cutoff point for both creating and maintaining competitive, democratic, wealthy societies may very well be over 90 and it's naive to dismiss IQ as a significant factor for why some nations are underperforming.

(4)

Not really, it's just that you dismissing entire populations as 'low IQ'.

I know what a normal distribution is. A more charitable reading of "Low IQ populations incapable of creating their own functioning societies watching western nations over the internet and worshipping it like some sort of promised land" would be "The people of nations where the average IQ is low are watching western nations over the internet and some of them, presumably the midwits and lower IQs of thier societies, worship it like some sort of promised land".