Yaarel
🇮🇱 🇺🇦 He-Mage
As your post acknowledges ...
The Flan are fantasy versions of Indigenous Americans, in the same way that the "Barbarians" are fantasy versions of Viking Era Nordic Peoples.
As a formula, a "fantasy" version normally combines something familiar with an element that is unfamiliar.
The disrespect can be in form of culturally appropriating, misrepresenting, demonizing, disparaging, humiliating, or dehumanizing via a stereotype.
The fact that the reallife familiar cultural characteristics are recognizable, makes it irrelevant if an unfamiliar element is combined with it.
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.
David Howery's adventure, "Ghost Dance," in Dungeon Mag #32 (1991) only reinforced the "indigenous North American" image of the Flannae.
So there certainly is evidence to support your argument.
The Living Greyhawk Gazetteer has art that again makes the Flannae vaguely resemble indigenous North Americans
The Flan are fantasy versions of Indigenous Americans, in the same way that the "Barbarians" are fantasy versions of Viking Era Nordic Peoples.
As a formula, a "fantasy" version normally combines something familiar with an element that is unfamiliar.
To use elements from reallife cultures in a disrespectful way is problematic in itself. Sometimes racist.The Flanaess is a fantastical world inspired by medieval Europe, peopled with pseudo-Vikings, pseudo-Huns, etc.
The disrespect can be in form of culturally appropriating, misrepresenting, demonizing, disparaging, humiliating, or dehumanizing via a stereotype.
The fact that the reallife familiar cultural characteristics are recognizable, makes it irrelevant if an unfamiliar element is combined with it.