"How were the communists able to promote an
anti-ethnocentric worldview in predominantly white countries at the same exact time as the National Socialists then? If they could do it, then logically, nothing precluded Hitler from promoting an
anti-ethnocentric racial theory within Germany if he so desired."
I have highlighted your bait-and-switch in bold. Communists promoted blank slate theory as their anti-ethnocentric worldview. But National Socialism rejects blank slate theory on principle. As you say, National Socialism in order to be true to its principles would have to promote an anti-ethnocentric
racial theory. This, however, is much harder than promoting blank slate theory. Therefore the fact that communists successfully promoted blank slate theory at best implies that Hitler could also have similarly successfully promoted blank slate theory, but does not imply that Hitler could have similarly successfully promoted an anti-ethnocentric racial theory.
"Occam's Razor says that it's most likely that he just didn't know enough about racial theory to form the same conclusions that we have, and ended up falling into the trappings of ethnocentrism because of that informational gap, or perhaps just straight up due to bias"
I agree that Hitler probably had less information than we have about race, but it remains my belief that he knew (even if on intuition alone) that Rosenberg had screwed up badly, which is why:
https://en.wikipedia.org/wiki/The_Myth_of_the_Twentieth_Century#Influence_of_the_bookAdolf Hitler declared that it was not to be considered official ideology of the Nazi Party:
I must insist that Rosenberg's "The Myth of the Twentieth Century" is not to be regarded as an expression of the official doctrine of the party. The moment the book appeared, I deliberately refrained from recognizing it as any such thing. In the first place, its title gives a completely false impression... a National Socialist should affirm that to the myth of the nineteenth century he opposes the faith and science of our times... I have myself merely glanced cursorily at it.[7]
According to journalist Konrad Heiden, Rosenberg had given the manuscript to Hitler to vet before its publication. After a year Hitler still had nothing to say. Hitler gave the still-unread work back to him saying, "I feel sure that it's all right."[11]
As for Mein Kampf:
https://en.wikipedia.org/wiki/Mein_Kampf#Anti-Slavism_and_Lebensraum_(%22living_space%22)
Hitler described that when he was in Vienna it was repugnant for him to see the mixture of races “of Czechs, Poles, Hungarians, Ruthenians (Ukrainians), Serbs and Croats, and always that infection which dissolves human society, the Jew, were all here and there and everywhere.”[20]
this is a consistent anti-Turanist attitude (almost identical to what I promote here, by the way). To portray Hitler as an ethnocentrist, your only remaining option is to argue that Hitler was a narrow Germanic ethnocentrist who considered even speakers of other branches of PIE-derived languages too ancestrally distant from speakers of Germanic languages. But then:
He also wrote that he viewed the Japanese victory over the Russians in the Russo-Japanese War in 1904 as a “blow to Austrian Slavism”.[21]
That he was happy about this makes it impossible for his worldview to be based in any kind of ethnocentrism (unless you want to argue that he believed that Germans and Japanese had common ancestors not shared by Russians).
"I think Aryanism should be able to stand on its own without Hitler"
I am confident that it already does. But that doesn't mean we should try to distance ourselves from Hitler either. The reason why most present-day leftists are misguided is because they still believe Hitler was the bad guy in WWII. Without clearing this up, all leftist rhetoric will continue to sound confused (e.g. comparing Israel to "Nazis"). If we were to stay silent on Hitler, eventually we will get (possibly well-meaning) leftists joining us who start to use similar rhetoric, which will surely corrupt our movement. It is to
scare away such leftists from joining that we make such a big show of holding up Hitler as one of our heroes.