Okay this is being analyised by people who don’t know the setting, and so they analysize using insectionality, which leads them to false conclusions, let me explain.
The Contients we know about are Faerun (mostly persuado europe), Kara Tur (persuado Asia), Zakhara (persuado Middle East, with abit of India in parts), Osse (persuado Australia, precolonization), Maztica (persuado Mesoamerica, very limited colonization, not particulary successful colonization), Archome (persuado North America pre colonization), Returned Abeir (weird area that likely returned to Abeir).
Here is the deal Chult isn’t supposed to the Forgotten Realms analog to Africa, that would be a large continent to the south, called Katshasa where the Chultans originally come from, having converted and summon by the God/Primordial Ubtao so the “Chultans” WERE the colonizing people, who partly displaced the Yuan Ti who were the indiginous population of Chult.
Chult is themed as a “lost continent” aka Sir Conan Doyle, but still a part of Faerun.
Yeah in FR the “Africans/Katasa” colonized “Europe/Faerun” but a Europe with greater biodiversity, and which already had a Native Black population, the Turmish.
The Chultans started out as a cultural diverse group of tribes, but eventually under verious pressures, merged.
The why Chultan culture appears to be a Blend of Cultures from Katasha, just as the various Shou Communities in Faerun are a merging of Shou Lung, Tu Lung, Wa, ect... cultures from Kara Tur, but they are very seperate in Katasha and Kara Tur.
Now the Turmish are native to Faerun, where they are large minorities in Mulhorand, Unther, maybe Chessenta.
But the Turmish are a Majority in the nation of Turmish, which is the only Major Democracy in Faerun and the home of the Emerald Enclave, which is the most powerful enivormental group in Faerun, lead by Druids. They are lead ruled by The Assembly of Stars, which is the legislative body of Turmish.
Turmish culture is African in clothing fashion, but peoples names sound Italian, I don’t know why.
Turmish and Chultans do not seem to be related, dispite both being black peoples, I don’t know why.
In Katasha Ubtao isn’t worshipped, they have their own Gods.
We have never seen current Katasha, no one from Faerun visits there in current times, so we don’t know what it looks like, except its African in Flavour.