You've referred to a few people claiming that the Germans didn't have a Jewish extermination plan in their concentration camps. I recognize a few of the names, I don't have time to look up all of the unfamiliar ones.
The Nazis ran 4 types of detainment camps, lets call them Concentration, Work(forced labor), Extermination, and Transit
As it became clearer that Nazis would not win against the Allies, the Nazis stepped up efforts in the Extermination camps.
As far as I know, the American forces only saw the results of the detainment camps, and never got to the extermination camps (they were in territory that eventually was held by the Soviets).
There's a good book on how the empires of Hitler and the USSR squeezed between them the jews and slavs of Eastern Europe, resulting in millions of deaths, "Bloodlands"