The rate and which the camps spawn barbs is very very slow, and mostly backward era units compared to the rest of the AI's and me. (warrior spawn in renaissance etc..)
Since I usually go Honor at some point, I can see the rate at which new camps spawn. It's slow also. It's been a long time since I've played a game with 'normal' barbs, but I suspect 'raging' isn't working at all, and what I get is just 'normal' barbs.