It would be better as an independent power given its population.
Honestly any "too low population" takes have always been in the losing position given the series have long featured NA tribes which population ranged between like 10 - 50 thousand (Iroquis, Shoshone, Sioux in civ2, iirc Cree)... Civ4 tried to circumvent this by the abomination known as "Native American" civ combining all of them, but it was agreed such cure is worse than the disease

Zulu kingdom, Maori, Mapuche and Venice also had population sizes of like few hundred thousands, so not that much better.