"Unprecedented" in that Jews had always been able to survive the various pogroms and other atrocities committed against them in the past. The survivors I talked to spoke of enduring (Jews are good at suffering) their captivity and then once the war was over, things would go back to "normal".
"Unprecedented" in the size (sheer numbers) and the industrialization of the genocide.
Sorry, I am still unconvinced that the Nazi mass murder of all the European Jewry they could get their hands on was unprecedented, unless you mean, "this time it happened to Jews". Oh, I don't quibble with the canonical Jewish death toll of 6 millions. Genocide is just too common an event in history and done in proportions greater than that inflicted upon European Jewry.
As for absolute numbers, the Nazis could not compete with the USSR(1) or Red China(2). Proportion-wise, there are many who are remembered only in history books, as their genocide killed 100% of them (or close enough that they were no longer a coherent people). Heck, depending on whose estimates you used, the Amenian genocide killed a greater proportion of Armenians than Jews were killed int eh Holocaust. And as for rate, the Hutus in Rawanda set the standard in the 1990s: 500k to 1million in 100days. Mostly with machetes, for a total of roughly
70% of the Tutsis in Rawanda. All that is just a partial accounting for the 20th century.
And if the focus is middle-man sojourning minorities, there have been plenty of (dot) Indians mass-murdered and completely wiped out in a particular country in Africa by bantu or nilotic peoples. Don;t forget the overseas Chinese in SE Asia killed to a man by angry locals at times.
I will grant a partial "unprecedented" for industrialization. Soviet genocide was pretty darned industrialized and started earlier than that by the Nazis, but the Germans were more efficient.
There have not been 144 narrative (fiction) films and 180 documentary films about, say, the Armenian genocide to drive the impression that the genocide of the Armenians was an unique event in history. Maybe if there were it would be the Armenian genocide we would look on as unique and the Turks as uniquely evil.
https://en.wikipedia.org/wiki/List_of_Holocaust_films(1) Ethnic Russians or minorities in the USSR.
(2) Han chinese or minorities in the PRC.