But yea, B/X works fine as long as you're willing as a group to not think too hard about NPCs and how they work. The fact that a fair number of players DID want to do that extrapolation is one of the things that drove the development of alternate rule sets.
Diversity is great!
But I'd also point out ... that most players don't care. The players that care usually become DMs to do the world-building, and then those DMs become really disappointed when they make all this detailed world-building, and then realize that .... guess what, the players don't care.
And the fact that so many people today now look back at B/X (Moldvay/Cook) specifically as an example of how rules were done correctly back then probably speaks to something.
Personally, I remember that at the time, I thought "Race as class? That's for babies!" Now I think ... "Eh, I can appreciate that."