I'm inclined to agree.
I very much dislike fantasy settings where you can point at the map and go, "That's Egypt. That's Africa. That's France. That's Greece. That's the Italian city states. That's pre-unification Germany. That's Arabia.", and what not.
Sometimes you see a quasi-European setting where the individual nations have no direct European analogue, and then surrounding it are stock 'Egyptian', 'African', 'Chinese', 'Japanese', 'Arabian' nations. That's annoying to.
I can see why you'd do it. It's very hard to create a body of material as compelling as a real world culture. It's very hard to imagine something that has little or no real world analogue. Also, its alot hard to invent novel permetations of a culture you pretty much know only through one or two stories, than one which you yourself are steeped in from a wide variaty of sources.
But it would be nice to see.
I used to try and create my own fantasy cultures. It's a lot of hard work for little reward - unless your players
want to read your hundreds of pages of notes.
In the end I found the easiest thing is to take our modern liberal democratic ideals, throw some real-world window dressing on them and call it a fantasy culture.
So you've got the western liberal nation that lives in the jungle and dresses like the Aztecs, the western liberal nation that lives on an island and dresses like the Samurai, the western liberal nation that lives in the desert and builds pyramids for their Pharoah, and the western liberal nation that lives in temperate climates and dresses like medieval Europeans.
Obviously the extent to which you can diversify depends on your players' understanding of real-world historical cultures, so if you're a bunch of Asian history majors you can make the distinction between Han Chinese, Japanese feudal and Srivijaya-era Sumatran cultures.
But if your players don't know the difference then what's the point? Save time and just throw them into the gameworld region your players understand as 'Ancient Asia' and get on with it. If your players have a better understanding of the difference between ancient European cultures (eg. Vikings, Celts, Angles, etc) then detail those instead.
But really, in my experience, going into too much cultural detail detracts from gameplay at worst, and at best is lost on all but the most curious and immersive of players.
Not to mention the fact that real-world historical cultures developed over thousands of years, and even my own has changed considerably since the time period on which I loosely model my game. To think I could ever have enough of a grasp of even one of these cultures to be able to portray every significant element for my players is the height of hubris.
And that's just for existing cultures. How could I hope to create one wholecloth?
I'm a busy person. I don't want to spend all my time creating elements of the gameworld that I can just plagiarise from history.