"Many think them the descendants of the ecstatic sects that arose across the Ancient North in the days preceding the Apocalypse".
Keeping in mind strange issues with dunyain genetics (no signs of inbreeding after 2000 years in total isolation, real difficulties in mating with humans), always saw them as apocalyptic mix:
1. First element is real dunyain refugees (from Sauglish?). 100% humans, members of a tiny cult, few in numbers & prone to domination, future base for a social peculiarities of a dunyain.
2. Second element is a Consult project gone rogue, numerous & docile, future base for a biological peculiarities of a dunyain. They look like humans and think of themselves that way, but Inchies and/or Mangaecca played with their genes with tekne.
It sounds both unholy & consulty to me — if immortal person capture mortal humans for some sinister purposes, why don't make them also impossible to inbreed and just spawn-spawn-spawn them carelessly in kennels, creating a steady and vast local supply? Lab rats, rapey-slaves, 144k stuff etc., lots of consulty uses.
But then we have Seswatha sneaking both in and out of the Arc. A kind of security breach, a possible situation for a large crowd of people (who can take flying arrows with their hands, lol) to simply walk out of Golgotterath and head in all eight directions. Some of them who walked south-east winned the prize, stumbling upon cunning runaway monks.
So, here's the irony, Consult's undoing will eventually come out of their own "lab rats", who survived for 2000 years right under Consult's nose.