I doubt that if the Nazis had won they would try to argue that all the crimes of the Nazi regime were committed by all the other Nazis and that Hitler was completely innocent of them all!
The point is not simply that Irving's history is biased: it is that he deliberately distorts the evidence or suppresses contradictory evidence of which he is aware. Thus, the court case consisted not of showing that Irving made statements in his books that were wrong - he could, after all, have been mistaken. It's that he made statements that he *knew* to be wrong. So, for example, he quotes a sentence from Goebbels' diary that supports his view and "overlooks" a sentence immediately following that contradicts his view. It is true that all writing of history involves assessing evidence and turning it into a narrative that may or may not be accurate, but good writing of history involves doing this honestly, that is, trying to take into account all relevant evidence and not simply ignoring anything that doesn't accord with your pre-conceived ideas. Thus, Irving doesn't "discuss" or "review" a reconstruction of the past, he simply makes one up and suppresses evidence that contradicts it.