I really, really have to disagree here. "Nubian" is an entirely inappropriate name for this religion, which was never practiced among the peoples that are today called "Nubians". Modern Nubians and their language(s), eg Nobiin, arrived in and came to dominate the region only in late antiquity, moving in from further west. They had their own traditions, and near as long as they've been known to inhabit that area, they were already Christians. The Kushite religion as expressed here does indeed stem from the Kingdom of Kush, the dominant population of which most likely spoke a Cushitic language (or several), as understood from loanwords into the Nubian languages, from more or less the only solid and secure ground we have for the Meroitic language (phonology and phonotactics, compared to contested attempts at translation), as well as material continuity, the historical record attesting the late arrival of Nubians, and Kushite burials showing physical and genetic traits distinctive of Cushitic populations. The Nubian peoples are believed instead to originate from around Kordofan and Darfur.
As it stands in Crusader Kings, the Kushite religion is dominant among (and, presumably, patterned after) the Beja, one of the extant Cushitic peoples, who were never Christianized and were only Islamicized in the 14th-15th centuries. The only connection it has to Nubians is that the area of the Kingdom of Kush ruled over had been called Nubia centuries prior to the domination of the region by modern Nubian peoples, who are today named after the region, not vice versa. Connecting modern Nubians to ancient history is a very common but very critical error. In antiquity, the Cushitic languages are believed to have stretched from the southern borders of Egypt all the way down to the African Great Lakes in an unbroken chain, and their presence is believed to have greatly influenced the region through the introduction of pastoralism to far southern groups (Khoi-San) as well as having cemented it in Northeast Africa, as well as potentially having been the origin of the domesticated camel.
While the religion may have survived the initial settling of Nobatae in the area, it did not do so for long. As the Nobatae kings bragged of driving the Blemmyes (Beja) into the desert, they soon Christianized their former lands and abandoned any semblance of Nilotic-type (Egypto-Cushitic) religion that they might've once practiced. As the religion in game is connected to the Kingdom of Kush, propagated by Cushitic peoples, was greatly reduced by the modern Nubian peoples suppressing revolts and wars of the Blemmyes against the Roman Christianization of Egypt, and by the game's starting date is more or less exclusively (historically) practiced by the Beja, a Cushitic people (though it seems the Daju might've been swept into it as well?), I think "Kushite" is an entirely reasonable name for this religion. If it is conflated with the Cushitic peoples, so be it - that much is as accurate as the "Germanic" religion being associated with a handful of Germanic peoples in CK2 (Saxons and Norse), even if not all of them (German, Suebi, Frankish, Lombard, Anglo-Saxon).
I've always been interested in the region's history so I am more than aware of the distinctions you brought up, but I was thinking of Nubian in terms of the name of the region of Nubia, rather than the modern ethnic group. Additionally, I wasn't aware that the flavor of the "Kushite" religion was explicitly stated in-game to mainly take inspiration from the Beja given that it appears both the Beja and Daju follow it (haven't really bothered to watch most of the preview videos or articles) though it would make sense given there's probably more sources for the Beja than the Daju out there (but I'm guessing this is similarly to how Germanic in CK2 was mainly inspired by the Norse, until at least Charlemagne when a bit of Saxon flavor was thrown in).
I do agree that even in that context that Kushite is a better term, so, fair enough, and, as I mentioned above, nobody outside of some historians and anthropologists would think the Cushitic language group first before the ancient Kingdom of Kush.
- 2