> It is only the mash of Hindi-Urdu called Hindustani [1] (popularized in modern day by Bollywood) that's mutually intelligible to both Hindi and Urdu speakers alike, and only in its spoken form.

Hindustani is not a mash of Hindi-Urdu that came into popularity with Bollywood. The distinction between Hindi and Urdu is a modern political division. Hindustani predates that political division.

[0] https://en.wikipedia.org/wiki/Hindustani_language