It’s not about popular or sophisticated, but rather about correctness vs. full of edge-case issues. Elixir does only supply the functionality, where it can ensure correctness. That’s why NaiveDateTime does have more functionality than DateTime. Also NaiveDateTime clearly communicates that it’s a simple form of handling dates, which might be enough for some usecases. But doing DateTimes correctly is not simple as @Qqwy explained above.
As for your question about other languages. Afaik erlang does not supply any datetime calculations at all. JS (Date obj) doesn’t have any add/sub methods as well. Just a lot of setters/getters. For languages, which allow transformation of dates you might want to check how well they work before trying to compare it to elixir not giving you a way to do it correctly as well as incorrectly (for DateTime; NaiveDateTime would be the explicitly incorrect way).
