The author starts off with some numbers, then makes up some arbitrary numbers, and then claims they yield some other numbers, and compares these numbers to someone else’s made up numbers, at least six times.
However I have to agree on this point. While Antioch might make sense for Minas Tirith. Albeit to quite a limited extent since it was a sea port and a major trade center being one of the last stops on the silk road.. While Minas Tirith was primarily a fortress which was probably not self sustainable on its own without food, wealth and population transfers from the other provinces in Gondor (so more like Constantinople just with massively less trade and built on the side of a mountain).
Edoras seems like a completely different type of settlement in almost every conceivable way and should probably be compared to Eastern or Central European towns.
In Lotr, Meriadoc Brandybuck is the halfling who swears allegiance to King Theoden of Rohan in Edoras.
The analogy doesn't go too far though, as the Rohirrim came from the vales of Anduin, near the Grey Mountains, while Conan's settlement, if it happened, was on return from defeat outside Rome. He was from Wales before that.