The problem is that once you have a world with monsters, it's no longer like the real world. And so authenticity is just an illusion.
If monsters were real, they'd likely move and migrate just like humans. Unless there was someplace really inaccessible, like Australia or they got exterminated in an area, like horses in the Americas or Lions most places but Africa.
Sure, authenticity is an illusion in the sense that it is purely in the perception of the players. But that illusion matters for the feel of the game. I could make a game that is historically accurate to 15th century Britain, but it has anime-inspired psychic powers and alien monsters. That could be logically consistent and fun, but for many players it wouldn't *feel* authentic to 15th century Britain.
To YOU (you have the right to be wrong) putting Inca Emperor mummies right next to European style vampires in a pseudo-Incan setting gives it "authenticity". To others it doesn't, it can be fun but it doesn't feel right, hence why people resort to re-skining monsters into something that feels like it belongs when they're not going for the gonzo approach (nothing wrong with gonzo mind you).
Now, I'm not saying every damn setting HAS TO BE "historically accurate", Al-Qadim, Kara-Tur & Maztica to name a few are perfectly fine settings and lots of fun can be had on those, but they are built to allow for the kitchen sink approach.
If what I want (and what I think Jhkim is searching for) is a high fantasy setting that feels like Inca/Aztec/Maya/Generic precolombine culture then that approach doesn't work. You have to work harder to create/addapt the races, classes, spells, monsters, etc for the setting to feel "authentic". I know because my High Fantasy Mayan inspired game is taking a lot of hard work (I might end importing stuff from other precolombine cultures).
I largely agree, but I'd clarify some. GeekyBugle is working on something that sounds more authentic than what I'm trying for. In my campaign, I am intentionally and explicitly setting a low bar for authenticity. But that still means there is some authenticity. I don't want kitchen-sink anything-goes, because I want to convey broad strokes of Incan culture even though I'm skipping a lot of the details.
I don't want to have all-new races, classes, magic, and monsters that fully reflect Incan cultures. That's not just because it's too much work for me, but because it would be a lot of work for the *players* to learn. That is why I am using a lot of the standard D&D races, classes, magic, and monsters. This limits the difficult learning curve.
In my game last night, I conclude that I messed up by my own standards. When going into the vampire's ruined lair, I included a banshee. It was reskinned to relate to an Incan myth, but a player commented that the banshee broke his sense of culture since he felt concept was too tied into Irish myth. In retrospect, I agree with him.
So you're trying to find a happy medium between high fantasy Incan inspired and the kitchen sink...
Good luck with that, IME that's even harder than what I'm trying to do.
No, I'm not going for an "Authentic Mayan" (Whatever that means) RPG, It is high fantasy, it has MY equivalent to Dwarves (Clay People), Elves (Wood people) & Halflings (Monkey People) from my mangling of the Mayan creation myth. So they work sorta kinda what you already know but are different enough that they help to sell the Mayan feel.
It even has Steel, because Viking castaways... Yes, yes, it's not "Historically Accurate" but we don't know enough of my ancestors to even try such a thing.
BTW the Vikings went back with "mini" quetzalcoatls (haven't settled on a name yet) they learned to train and ride, plus Mayan astronomy and math, so if you ever play in MY version of Europe I think you'll find it is very different. The Mayas got from the deal the secret of making steel and seafaring.
Fuck I think in MY version of Earth, it will be Vikings and Mayas doing the colonizing. But that's not the time period the setting is dealing with, that's still in the future.