I don’t know if I just did that bad a job with the graph or whether we are locked into such opposite ways of thinking that we look at the same idea and still see it differently. “All evidence is a mirror” I like to say.
Well even though it has consisted of questions and I am not sure you ever got what I was trying to say, you did engage on my graph so I should also say something about yours. I don’t think you get an accurate picture just by looking at a graph of hominid brain sizes. Many mammalian orders showed a marked increase in brain size during this same period. Modern gray wolves have larger brains that dire wolves. Indeed this study of the order Carnivora show that the vast majority of the order was undergoing the same process your graph shows occurring in hominids.
Now it is known that brain size in modern humans is if anything decreasing. And it is in domestic animals as well. One doesn’t need as much general intelligence to follow the herd as to to make it nearly on ones own it seems. But the main point I want to make is that brain volume doesn’t tell the real story. Indeed since I believe in a supernatural realm the physical construct of the brain doesn’t tell the whole story - and that is a more reasonable explanation for the vast differences in accomplishment and civilization building when comparing us to them. Nevertheless the brain structure is different between humans (to me only Sapiens are humans) and other hominids and this difference is quite recent. See the link from this thread about how recent our globular brain shape is…(though I have theories about that too)