I'm pretty skeptical that cultural change was meaningfully slower (except as limited by effective population sizes). Cultural change for early humans is nearly invisible in the material record. Imagine that all archaeologists of the far future find nothing from the current era except iphones without working storage. Do they indicate a unified global culture without cultural change outside WWDC?

Obviously not, even though there are aspects of a shared global culture indicated by their global distribution. Material culture is related to culture, but it's an imperfect and imprecise record. The same issue occurs with correlating culture with genetics or language.