I was going to say the same thing, but then I realised the initial claim was also about 'cultural unity'. So fair enough, and yes a lot of Europe (or all of it in a few sections) has been culturally unified since time immemorial.

It is a bit more complex though, certainly even today there's some very distinct 'culture' in different regions across India. But also shared themes and roots (e.g. Sanskrit & texts written in it, from which modern 'distinct' languages/beliefs/teachings have been derived) that kumarvr's far better placed to comment on than I am.

To go even further: I imagine if the Arab world was politically unified with Europe today, there'd be a lot of people saying that it was always a unified Mediterranean cultural entity, sharing Monotheistic Abrahamic religions, Greek intellectual foundations, and having a long-term shared history in the Roman world. It's not a point of view commonly encountered today, though, probably because Europe and the Arab world aren't politically unified.

That is to say, if you decide that a region should be seen as unified (perhaps because of modern political boundaries), one can cherry-pick common elements to try to reach that conclusion. It's not entirely incorrect, but it's a biased way of presenting the evidence in order to justify a preconceived belief.