I wouldn’t. There are NPC shamans and warriors and scouts and spirit warriors and the like. They don’t need PC class levels.
But I’m not trying to argue about whether the assumption is reasonable, just wondering what the impact would be from something closer to what the game seems to assume.
I would think 1% of adults in a wilderness tribe would be the normal PC classes in the normal. 5-25% would be NPC noncommoner nonnoble classes. Their level depend on the setting.
But if you boost it, I could see a 300 adult village having at least 10 fighters and barbarians in it.