We now know ( from ancient DNA) that Bushmen split off from the rest of humanity (or we from them) at least a quarter of a million years ago. Generally, when you see a complex trait in sister groups, you can conclude that it existed in the common ancestor. Since both Bushmen and (everybody else) have complex language, one can conclude that complex language existed at least a quarter million years ago, in our common ancestor. You should also suspect that unique features of Bushmen language, namely those clicks, are not necessarily superficial: there has been time enough for real, baked-in, biologically rooted language differences to evolve. It also shows that having complex language isn’t enough, in itself, to generate anything very interesting. Cf Williams syndrome. Certainly technological change was very slow back then. Interglacial periods came and went without AMH displacing archaics in Eurasia or developing agriculture.
Next, the ability to generate rapid cultural change, invent lots of stuff, improvise effective bullshit didn’t exist in the common ancestor of extant humanity, since change was very slow back then.
Therefore it is not necessarily the case that every group has it today, or has it to the same extent. Psychic unity of mankind is unlikely. It’s also denied by every measurement ever made, but I guess invoking data, or your lying eyes, would be cheating.