"Barbarian" cultures like Huns, Goths and Mongols make sense because they took over urbanized empires, but is the same for Sioux, Maori and Zulu? Would not these later cultures make more sense as minor ones?
Honestly, every "barbarian" civ which managed to be powerful and organized enough to be a massive, existential military
threat to huge empires gets a free pass from me. Such as Scythia - they didn't even break empires like cultures mentioned by you but I support them in civ by their sheer historical weight, also they had far more refined culture and art than "stepper savage" stereotype may suggest. They really had an enormous impact on Eurasia - on China, India, Middle East and Eastern Europe, by trade, culture, military, them being probably original inventors of cavalry (especially mounted archery) etc.
Precolombian urban peoples also get
the pass from me - in their case they had sheer bad luck of being isolated, but they have some unique massive stories to tell (such as ancient Pueblo and Mound Builders in US, with their massive architectural works and trade networks spanning across the continent).
US Native tribes, Mapuche, Maori or goddamn Zulu don't get this pass from me because they were, well, minor. They had no big importance for history, they were just relatively "backwards" if rich cultures which had some degree of success defending their ancestral lands before finally an industrial empire crushed them inevitably. This just doesn't make for very unique or impactful "story". Mapuche at least managed to defeat Spaniards and Incas for centuries, so they had ridiculous success. Maori are sort of representing far larger phenomenon of Oceanian peoples who were the greatest sailors in history. Lakota and Comanche were incredible cavalrymen (especially regarding how late did they get horses). But... They all still feel wonky for me, as "should have been a minor civ in some way, this is just not the same category of societies as the Ancient Egypt".
They also don't really inspire very realistic and interesting designs (like what, you'll give them all "homeland defense bonus especially in difficult terrain")? And instead they get some fantasy bonuses enabling them to conjure cultural energy from sacred terrain, or be insanely good at extracting industrial value from it (better than 20th century tech), neither of those sounding very good for me.
Civ4 "Native Americans" (what an abomination
) literally had defensive and spirital focus, civ5 iroquis had magical powers in forest, shoshone had homeland defense bonus, civ6 cree have magical powers in forest, mapuche have 3/4 of their design built around "homeland defense" trope, Maori have magical spiritual terrain powers in general, and Zulu have always had the exact same design in every strategy game ever released, the most boring faction ever. If those two traits I have described (or the third trait of vaguely powerful tribal warriors like Zulu) are everything you can think of when trying to add a culture to the game, maybe it really should be minor faction, if it can be only translated in terms of the most universally human traits which happen everywhere ever:
- humans fight bravely to defend their ancestral homeland
- people who live in that terrain are of course more experienced at exploiting it (by the way I am very skeptical of civ6 claim that Maori are very "ecological" culture but that's separate issue)