To be clear, in general the vocative is a case eg in Czech and other balto slavic languages (except eg standard Russian while colloquial Russian is developing a new unrelated one).

In Latin tho, it's more a relict. Other cases have relicts, too, still I wouldn't say Latin has the locative.

I would argue that being a relict is a spectrum. Technically, it is a case with many syncretism to nominative, since it is obligatory for those nouns. In the context of LAtiN hAs sOo0 ManY cAsES, it's not.