I mean, okay, maybe real world Steppe peoples would have been subject to variations in dialect. Do I need pages of stuff telling me that the absence of a sentence like "Dany couldn't understand that one guy very well because he spoke a confusing dialect of Dothraki" is a glaring oversight? If there's one thing the series doesn't need it's a whole other novel that goes even further in detailing the misery of navigating the cultural differences on Essos. One ADWD is plenty.
As a reader, you certainly don't need that to enjoy the books.
But since GRRM claims that the Dothraki are based on reality "seasoned with a dash of pure fantasy" it's worth pointing out that based on what's actually in the books themselves it's the other way around: the Dothraki are fantasy seasoned with a dash of reality.