It is an interesting thought exercise in my opinion Khuxan.
The problems that I see with an Occidental Setting and with D&D in general, per se, are exactly what you and others have implied, the problems of Era(s) [time], and geography(s) [space].
I run a semi-historical D&D milieu set on our world, circa 800 AD, and the geographic base of operations is Constantinople. We use real world religions, cultures, politics of the time period.
It is a D&D game mostly, with milieu and historical modifications I have written myself over the years. But the trouble with D&D and OA in regards to history is that one has to define exactly what one means by accuracy, and in regards to what time, and in what area. Eastern Europe and the Bulgars were extremely different from the Franks and the Carolingian Empire. The Russians far different from either. The Russians even different from the Vikings, though both were of same stock. The Italian city-sates, like Ravenna, not like their Roman and provincial forbearers. The Romans of Byzantium were nothing like the Romans of the Republic or Western Empire, and the Byzantines of the age of Justinian little like the Byzantines of the era around the Fall.
Also, do you include Africa in the Occident? Places like Carthage, Egypt, Libya, even Ethiopia played a large role in the West of the Romans and even of the Occident of the Byzantines. Are you just going to concentrate on Western Europe when one says Occident? Is Romania occident? It was after all named after Rome. What about the near-east, in which places like Syria and Israel and Palestine and even Persia were fundamental to the development of the Western Roman Empire, the Byzantines, and even to Western Europe? Would you include Islam as definitely Occidental, influencing the Occident, or Oriental in thought and nature?
The trouble with both D&D and OA (and I have OA too, and like it as a basis for developing more historically accurate game character models) and history is that both the time-frames and the geography are so sweeping that they cannot possibly be historically accurate specifically (or encompass real accuracy), though I think both efforts extract many important historical elements to create Cultural and Religious Game Archetypes.
If I had to describe it I would say both efforts cast a wide net, rather than a deep one. That is to say they are more interested in "sampling" some of the more important religious, mythical, and cultural Archetypes, over a wide range of geographies and historical eras, than they are interested in being accurate "in-depth." Which is another way of saying that the games wanted to embrace a lot of different possible milieus within one game umbrella, rather than concentrating on specific eras and geographies. Which is another way of saying the games wanted to reflect general cultural backgrounds and tendencies, but did not want to be tied to any specific milieu. They wanted to be milieu flexible.
Yeah, I think sampling might be a good way to put it. These games are not interested in detail as much as with "feel" and creating a sort of loose archetype of famous ideas and ideals (like with the Paladin).
If a D&D game had been designed by an Oriental writer or writers, rather than by Gygax (and the original D&D game was heavily occidental in basic modality) then I think they may very well have used some of the same tropes (though with different nomenclature, Paladins would have become Knights, Clerics would have become Priests, and so forth) and some very different ones (strict monotheism would have likely seemed exotic and fascinating in some ways to many Eastern minds in the same way paganism and polytheism might seem historically foundational in D&D sampling, but by the time era most of the original D&D "classes" - and they weren't really classes but rather professions - were structured then paganism was already an historical anachronism). For instance the Cleric is obviously not written to reflect paganism, but Christianity, so was the Paladin, a distinctly Christian cultural and mythical form and ideal. Nevertheless paganism was adopted as an anachronistic religious type or mode in D&D. It would also be very interesting to think of how an Oriental writer would have approached the idea of class and station very differently than Gygax. Gygax uses class to only very loosely and vaguely reflect what real class was, a social station. Instead he uses it really to describe profession or "vocation," - the Cleric, Paladin, Ranger, and Wizard all reflect the idea of the "vocation." The East, generally speaking and up until recently has been much, much more fixed upon real and more historical and cultural class-ideals than has been the West. The West basically abandoned class, or made it anachronistic, long before the East, because of religious, economic, and political reasons. (Instead many in the West were far longer fixed upon the idea of race, rather than class, in a way making race a sort of "de facto class" in many cases.) It would be interesting to see how Eastern writers would have reinterpreted class in-game based on what they think it might have meant to the overall history of the West.
It would be I suspect an interesting exercise to "interpret the West" from outside and to see what some Easterners would have thought of as the most distinctive archetypes of the West to build a game around.
