Maybe. Or, maybe you can look at what was the existing knowledge base of society, what was the population, what transformational changes did society invent and with what frequency, especially when compared to peer societies, and when did a society go from being a thought leader to cannon fodder.
It is an exercise where you compare them against their contemporaries, not an modern IQ test. The IQ portion is an estimate of what level of IQ would society have needed to average to make the types of transformational changes at the speed with which they occurred based on the size of the population.
“and when did a society go from being a thought leader to cannon fodder.”
Good points. If this claim is true, then it also happened around the time Rome ditched the republic for imperial dictatorships.