That's an interesting theory, but history just doesn't support it.
History supports itself. It is the winners that write history. Archeology often contradicts history. Much of the bible, after all, is history but it's not necessarily true.
Many credit Romans with civilizing Europe and building the roads etc, but that's because the Romans said they did and wrote about it. Archeology says it's not that simple. Similarly Britain was a great and glorious empire civilizing savages and putting our brave boys on the line to do this selfless work.
All public and national histories are mythologies. There are histories that hove much closer to fact but they tend to remain locked away for academic reference rather than general consumption.
There is no shortage of examples of people being conquered and yet maintaining their roots.
Of course, because they maintain their own histories. It takes more than force to wipe out a people's histories. The Jews have maintained their own version of history over centuries which has been integral in keeping a separate identity. but, you catch more flies with honey than vinegar, they say. Hitler had crafted for his reich a compelling history which doubtless he could have expanded to include the lands he "freed".
It would probably be not far different from the myth that we constructed for ourselves about how "we" freed Europe, despite the fact that we committed atrocities in doing so.
And if huge numbers of German troops died in US pow camps and no one ever heard about it, how did you hear about it?
It isn't unknown or lost history. It's simply not talked about much because it doesn't serve the heroic narrative.
And we do know about the aerial bombardment of Germany (Dresden in particular) and the nuclear bombs in Japan. Those are both nasty thigs you'd think they wouldn't want us to know about and yet, they're in all the text books. Go figure.
Both depicted as unfortunate but necessary victory to save Europe/America from an even worse fate.
But anyway, my main concern with your post was that you tell us that Hitler's only real sin was that he lost.
In a very pragmatic sense it is the only one that actually matters. Are our current owners really so much better than Hitler? Yes, you might say, because they aren't killing Jews - but they are killing other people - just far away people so we don't have to care and we aren't even allowed to see what it looks like to kill them. Hitler is the guy we are all supposed to hate but Churchill who was every bit as viscous is a hero.