One point to call out that the author doesn't emphasize is that steppe cultures (both in North America and Eurasia) were integral parts of vast trading networks. One of the noted features of pre-Columbian North America [2] was the extent and speed with which trade goods moved all along it. So steppe cultures would absolutely have access to all the fine luxuries of the "civilized" world. Indeed, it should be noted that marrying off royalty to steppe elites was a common strategy for keeping steppe raiding at bay. This is fairly evident to anyone who does even a modicum of research on steppe peoples, or ancient people in general (people trade! all the time!), so the notion that steppe people are inherently austere is clearly the mark of someone who does not believe in research.
[1] e.g., colorless white Greco-Roman temples: all the paint faded away, leaving the underlying white stone. When the Renaissance kicks off a shift in Greco-Roman historiography to putting them at the pinnacle of human civilization, the extant white ruins were taken as reflective of what they actually looked liked and became the archetypes of modern attempts to re-summit civilization's pinnacle.
[2] Although it should be noted that the steppe cultures of the US--such as the Cheyenne, Apache, Sioux--don't exist in their modern form before the introduction of the horse around about the 18th century, with the Siouan peoples not even living on the plains until pushed out there during migrations in the 17th century.