Good point. One may also add that other, non Darfari-Exiles might be reluctant to join a demon-worshipping cannibal cult. Although it’s all just speculation, your theory seems the most plausible to me.
This was originally planned for the game, but almost all of the racial bonuses have been removed. For some reason, not all of them were. Shemite and Hyrkanian thralls still get a +50% ranged damage bonus.
They do!?
You learn something new every day… That might explain why some thralls of the same faction have weirdly different stats.
Still, probably a leftover. Overall, stats are faction-based.
@ Stelagel
Some racial differences are still there. Darfari members of other factions are taller than their comrades afaik. Weird that their… uhm… positive character had differences, though. Maybe human flesh wasn’t good for their… health? It’s weird.
Oh you should see the surge ones sister 
. On Siptah my favourite Sourge waa always the South one , except the fact that they have a permanent tattoo, they are tough as hell.
One thing that must be noticed for darfari however is that before the change of the attribute system, all Darfari fighters had huge advantage and growth on the survival. I use to drag them with me on volcano missions since they didn’t die as easy as Berserkers on lava. Then poisoning from snakes was not so severe to them, but Berserkers were killing it so fast that it wouldn’t matter anyway.
Of course aa soon as you were getting a volcanic thrall , especially Spinas, then both Berserkers and Darfari were useless. Volcanic thralls had both endurance on lava , better hp from Darfari and hit hard as Berserkers.
Lesteret was the go to for me since he had all these bonuses plus humongous HP, but really rare find on purges.
Good days and beautiful memories, apologies for derail 
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isnt’ the Forgotten Tribe literally all Cimmerians ?
Also I like to think Dono’thelpup was separated from his Cimmerian comrades in the deserts from a Darfari ambush and he was made into a mule slave instead of being eaten/sacrificed