The Holocaust is much more than Auschwitz. The article discusses the problem of making Auschwitz emblematic of the Holocaust. We need to remember the mass shooting, liquidation of the ghettos, and the Reinhard camps too.
It seems to me that two-bit anti-Semite frauds can use Auschwitz to score points for total Holocaust denial because in the mind of the public, Auschwitz IS the totality of the Holocaust, and therefore, questions about past problems with Auschwitz are seen as problems with the Holocaust as a whole. As you pointed out, it’s “easier” to argue Auschwitz denial. But because of the tendency of scholars to (publicly) use Auschwitz to represent the totality of the Holocaust, it therefore becomes “easier” to deny the entire thing. It would be great if future generations, when encountering those who question Auschwitz in order to deny the Holocaust, could automatically respond by saying “but what about Treblinka and Sobibor and the Minsk Ghetto?” As you pointed out, deniers have a hard time dismissing those things…but the average person is usually not aware enough to bring them up.