Is the U-Tribe at the Forgotten Springs an outlier with Nunh Leadership?

[Velox]

It's left intentionally ambiguous. Also, they very explicitly specify patriarchal heritage for Seekers and matriarchal heritage for Keepers. This does not automatically equate to a patriarchal and matriarchal society, so we are free to speculate on what it might be and what is common.

The moogle mail questline involving the Lihzeh sisters and the Coeurlclaw King does back up SE's claim that Keepers do hold their value in a matriarchal society. The quest (coupled with a few sidequests and FATEs) even goes about explaining why (male Keeper genetics makes them better at being their own man rather than fathers/husbands, and really only stick around for breeding to keep family lines alive before leaving to wander again) and that what the King is doing violates everything Keepers stand for and threatens tribe and inter-tribal stability.

Now it's not a matriarchal society in which women force it though, more of one born out of "understanding" for how males work genetically. Women KNOW males are prone to certain traits and don't blame them for it, but rather, mold life around it to accommodate them in some way. Males get their freedoms while women run the tribes, raise the kids, set the laws, hunt for food, and negotiate trades with other tribes.

That being said, it doesn't explicitly say anything about Seeker tribes, so you may be correct in that aspect. But for now, we have a pretty good foothold on Keeper lore.