The only logical argument for "unconditional surrender" in WW2 was ideological. An idealist obsession with what happened after the enemy admits "you beat me" rather than getting that admission itself. There was no more long-term danger post-D-Day and post-Marianas turkey shoot from Germany or Japan. What would have been the alternatives to making nice with the west for Germany/Japan, an alliance with Stalinist Russia? LOL. Unconditional surrender was unnecessary because a German-Soviet or Japanese-Soviet alliance was impossible.
On a separate but related note, the Initial British intervention in Europe to guarantee Poland's integrity in the summer of 1939, made things much worse than it otherwise would have been. Had Britain remained neutral there simply would have been a Nazi-Soviet war over eastern Europe instead of the WW2 that we know; The Showdown between Hitler and Stalin would have been a bloodbath even worse than the historical eastern front, but the rest of the world would have been much better off. Instead Missionary generation washy-eyed idealists (the direct precursors of the current boomer globalists) forced their preferences down everyone's throats.
I'm afraid you're wrong. The "unconditional surrender" policy in WW2 was a way to avoid a repetition of the Dolchstoßlegende ("stab-in-the-back legend") used in the 1920's for denying any legitimacy to the Weimar Republic.
As for the beginning of WW2 in Europe, Hitler believed world history was a struggle between races and imagined the future as one of wars of conquest until Germany was the undisputed master of the whole world. So, had he conquered Poland in the fall of 1939 without a declaration of war by France and Britain, the question would have been if he had to strike France before the USSR or the USSR before France, something which in his mind was just a step before the big push for world conquest.
In another subject, I miss the old formula of daily reports.