My contention is not that what happened there was exaggerated, but rather that the evil it represented was not unprecedented in human history. The notion that the scale of killing was unprecedented in human history, and that "industrial processes" were needed to kill lots of people in a short time, or that the Nazis brought some novel degree of efficiency to the process of murder.
The Mongols killed 60M to 100M people, a MUCH larger percentage of the human population at the time than the Nazis and commies combined.
They also killed more people much faster than the Nazis, being rivaled in this only by the great bombing attacks of WWII.
The Mongols regularly took 100,000 or more people captive after taking a city, bound the captives and shared them out among a perhaps 50,000 man army. On the signal, everybody chopped heads and then they built a pyramid with them.
IOW, the Mongols routinely murdered 100,000 people in just a few minutes. Whereas, if I remember correctly the maximum killed in 24 hours at Auschwitz was somewhere around 25,000.
Since the Nazis had to ship people from all over Europe to Auschwitz, using precious shipping space to do so, their method of killing was immensely less efficient than the Mongols, who needed only edged weapons and tens of thousands of hardened killers willing to use them.
My point is not that the Nazis were not spectacularly evil, only that we have forgotten how much evil there is in human history.