Crematoria were only used on a minority of Jewish victims, that is why the 6 million could not have been 'disposed of' this way.
The vast majority of victims were just put into mass graves and buried, or burnt in the mass graves and then buried.
Also you forget that no one has said that 6 million were 'processed' in the camps - those killed during Germany's eastward advance were killed where they lived until The Nazis realised they were wasting bullets - that's when they decided to build efficient death camps and use gas to kill large numbers.
You also forget the Warsaw Ghetto, no camps needed, they just died of starvation, exposure and shootings.
The assertion is that the Nazis targeted and killed 6million Jews NOT that million Jews were killed in Death camps.

"Deaths in the Bible. God - 2,270,365
not including the victims of Noah's flood, Sodom and Gomorrah, or the
many plagues, famines, fiery serpents, etc because no specific numbers
were given. Satan - 10."