The people actually using the constant are translators.

What about India? They alone would reduce China from the 'vast' majority[0].

[0]: https://en.m.wikipedia.org/wiki/List_of_countries_by_number_...

Is this concept also used in any of the major Indian languages?

Yes in Hindi you have different nouns and adjectives for uncles, aunts and cousins depending on the relation path:

E.g. Mother's sister = Mausi

Mother's sister's child = Mauseri/mausera

Father's younger brother's child = chacheri/chachera

And so on.

Although some of these are more obscure and I'm not sure how commonly they are used these days.

I see.

Notably, mapping the entire path isn't congruent with the concept in the topic, which encompasses both "Father's sister's daughter, younger than me" and "Mother's sibling's daughter, younger than me" in one phrase.