I think it’s probably impossible to avoid referencing real-world cultures; we only have our own history upon which to draw, or our fiction which ultimately, itself, draws from our history in some way. We seldom invent anything from whole cloth.
D&D’s roots lie in medieval simulationist wargaming. From its inception, and for a long time, its tone and inspiration was primarily Northern European – whether directly, or moderated by Howard, Anderson, Tolkien and the like. It was also intrinsically Orientalist in its approach for most of its history, freely caricaturing non-European cultures in Blackmoor, Greyhawk and the Forgotten Realms – this tendency crystallizing most obviously in settings like Maztica or Al-Qadim. I think these are relatively uncontroversial assertions. I also think it’s reasonable to view these efforts as clumsy and naïve from the vantage point of 2018.
I believe that the OP’s post contains two overlapping ideas, and I think it’s probably worth separating them:
1) Campaigns set in a real-world historical context, probably with fantastic elements
2) Campaigns which draw on real-world historical cultures for inspiration
The first has always been one with which I am cautious to engage – I’m something of a perfectionist, and there is just so much damned work associated with accurately portraying an historical culture, that it can appear overwhelming. I’ve successfully run one-shots (or two-shots, or three-shots) in a variety of historical periods: 8th-Century Wessex; 12th-Century Anjou; 11th-Century Norway – or whatever. But these time periods and cultures are well-known to me, and well within my comfort zone; recently I’ve been toying with early Iron Age Canaan, but even finding an historical consensus on this period is close to impossible. I’ve tended to use other systems (Ars Magica, Pendragon) to run “historical” campaigns with multiple sessions – both of these systems are obviously dripping with fantastic and ahistorical elements.
I would argue that the second idea – that of campaigns which draw on real-world cultures (historical or contemporary) in elucidating fictional cultures in the game milieu – is essentially unavoidable. It therefore becomes – for me, at least – a question of how well I can disguise elements which I have appropriated from real-world cultures so that the players don’t immediately recognize them as a transplant from Earth history. I don’t want to say “they’re like Toltecs” or “they’re like Minoans” to the players; I’d prefer to maintain the illusion of originality :/
As a relatively privileged white European male growing up in the 70s and 80s, who had absorbed a good deal of Tolkien before being introduced to RPGs, I think my perspective was probably fairly congruent with that of the early game designers – I’m part of an early demographic, so to speak. As a teenager, I possessed many of the biases and internal stereotypes that my British Whiteness bestowed upon me, and these informed my playstyle. I hope I’ve shaken off most of those elements of my understanding, although I’m also sure some little nuggets of bigotry and prejudice remain – transcending one’s own culture is a life’s work.