This statement is inconsistent with your previous paragraph. The two
explanations also disagree about whether the missing Jews were killed,
or whether many, "perhaps the majority", survived. This is a far more
significant difference then the method by which they were killed. If the
revisionists agreed that the Jews sent to the camps were all killed,
but insisted that it was by mass shootings rather than gas chambers,
the debate would not have much interest and would probably be confined
to historians.
The real issue is the claim that many or most of the Jews were not
killed at all. This would significantly reduce the moral culpability
of the Nazis, while casting Jewish organizations and sympathizers as
villains, inventing a horrifying story like this without justification.
I believe that is the real agenda of most of the revisionists.
Hal