Regarding the balance between factions, I want to add that they are not identical with “races” or larger cultures - except for the Darfari for some reason.
The Forgotten Tribe isn’t Cimmerian, but copies Cimmerian culture. A Cimmerian can be a member of the Black Hand faction, and non-Cimmerians are part of the Forgotten Tribe.
Only the faction determines their strength, not their heritage. A Cimmerian in the Exile faction is very weak, a Zamorian from the Forgotten Tribe is very strong.
There is little ingame explanation for that in my view. Maybe, the NPCs “advance” through the Exiled Lands just as a player: Exiles are recent arrivals with little combat skills. And the most hardened Exiles are recruited by the Forgotten Tribe and Votaries. But that’s all head canon.
Anyhow, one shouldn’t mix up racial and cultural differences in Hyboria and the differences between factions in the Exile Lands.
If “racial” or cultural background would make differences in NPC strength, it would be connected to their race or culture, not their faction, e. g. all Cimmerian NPCs get +100 HP across all factions, Zamorians +10% agility weapon damage and so on.
But it’s not like that. In the game, race/culture seems to play no role at all.
The Darfari Cannibals are the sole exception, which leads to questions as to what that faction is all about. Where they exiled as complete tribes? Do they only accept Darfaris into their faction? Are they natural inhabitants of the Exiled Lands? I assume the latter, but there’s no definite answer to that in the game afaik.
Darfari in other factions, though, behave just like other members of their faction, so their strength (or lack thereof) seems to be faction specific, not caused by genetics or culture.