Flannaess drives from the earlier Castles & Crusades map that intentionally stylizes North America. The City of Greyhawk corresponds to Chicago and the Town of Blackmoor corresponds to a remote town on Hudson Bay in Canada, where the town of Churchill is.
The Flan are inspired by the reallife Indigenous of these same locations and elsewhere in North America.
The Flannae are the "native" "tribes" of Flannaess, who are "hunters", being the "first humans" to arrive in the continent. Their "bronze" skin ranges from red "copper" to dark brown; the hair black or brown; and similarly, the eyes "dark brown, black, brown", or for a touch of fantastic exoticism, "amber". Etcetera. These intentionally describe Indigenous Americans. Unfortunately, Gygax evaluates these Indigenous as having "made no appreciable civilizating efforts". Meanwhile, they speak "a stagnant language" that is "difficult to translate modern concepts into". Moreover, where he defines these ethnicities as human "races", his commentary is actually racist.
Illustrations that portray the Flan display Indigenous American material culture, even war paint.
The Flan are the fantasy version of Indigenous North America.
Using a map North America as the basis from which to trace the map of a fantasy world does not automatically make the indigenous peoples of the fantastical continent equivalent to indigenous North Americans.
And being Canadian, I guess I never realized that North American indigenous peoples were led by
Atamans (see entry for the Rovers of the Barrens, one of the few "pure" Flan territories left in the setting, as per p. 33 of the Guide; also see Gygax in Dragon Mag #57, pp. 13-14). How silly of me. I'll let my indigenous friends know right away so that they can correct their respective histories.
Yes, the description of the Flannae and associated art (to my knowledge, there's only one Gygax-era illustration showing humans of different ancestries, on p. 15 of the Guide) certainly could lead one to conclude that they are modelled after indigenous North Americans. I'm not sure how well that illustration matched Gygax's own vision for the Flannae, but that's a moot point. And David Howery's adventure, "Ghost Dance," in Dungeon Mag #32 (1991) only reinforced the "indigenous North American" image of the Flannae/Rovers of the Barrens. So there certainly is evidence to support your argument.
Still, the title "Ataman" suggests that Gygax had more in mind for the Flannae than merely making them analogous to "North American indigenous peoples" (which in itself is a broad overgeneralization of hundreds of different nations with different languages, customs, technology, beliefs, etc). And I can think of other peoples around the world among whom "bronze" skin, black/brown hair, and black/brown (or, less often, amber) eyes are common, who were/are accomplished warriors and hunters.
Here are a few quotes direct from Gygax, not paraphrases:
"Flannae. The Flan race have a bronze-colored complexion. This varies from a lighter, almost copper shade to a
very dark tone which is deepest brown. Eye color is commonly dark brown, black, brown, or amber (in declining order of occurrence). Hair coloration is black, brown-black, dark brown, or brown." (Gygax, Guide to the WoG, p. 13, emphasis added).
"The original Flannae stock shows up with either Oeridian or Suloise or both as a coppery or bronze overtone [suggesting the default coloration is "brown" or "deepest brown"]. . . A hybrid of Baklunish and Flannae gives a golden-copper or golden-bronze color which is possibly the most attractive complexion of any of the admixtures of the basic races." (Gygax, Guide to the WoG, p. 14).
So the "pure white Suel" aren't the paragons of human beauty according to Gygax or his unreliable narrator? Interesting.
The Living Greyhawk Gazetteer has art that again makes the Flannae vaguely resemble indigenous North Americans, but the Old Faith they purportedly follow (and the related Old Lore bardic colleges) have a more Celtic feel... and the Rovers are still led by Atamans. This once again confirms that, even in the post-Gygax era, the Flannae are more complex as a fictional race/ancestry than a cursory reading might otherwise suggest.
I'm not denying that there are problematic racist generalizations/implications in much gaming content, old and new (including in Gygax and the World of Greyhawk). I also approve of efforts to provide a deeper understanding of the complexities of racism (and other isms), and to foster appreciation for diversity in all its forms, both within our hobby and in society-at-large. I think you and I are on the same page with regards to this.
But I still think you're going too far in presenting your interpretations as fact, and in ascribing nefarious motives where none may have been intended. Racism in all its forms is unacceptable, but people unfortunately don't always realize when they're making racist statements or behaving in a manner that reinforces racism/racist stereotypes. And then, there's the issue of the unreliable narrator, which I wouldn't just hand wave away and claim with certitude that it's merely a reflection of the author's point of view.
I'll say no more on the subject.
EDIT:
Sorry, I lied. Just wanted to add this...
Riddle me this. Where did the first Europeans migrate from? What did they look like? How did they survive?
And where do archaeologists think the ancestors of indigenous North Americans came from?
I suspect that Gygax knew the answers to those questions when he developed the World of Greyhawk.
The Flanaess is a fantastical world inspired by medieval Europe, peopled with pseudo-Vikings, pseudo-Huns, etc. Stating that the Flannae are equivalent to indigenous North Americans because Blackmoor Town holds the same position on a map as Churchill, Manitoba (thanks for the geography lesson), and Greyhawk the same place as Chicago, doesn't confirm or deny anything, aside from your own interpretation of what it means to be "indigenous" in the Flanaess.