Yeah, raging barbs is great for slowing down some of those settler-spamming civs a bit, early on. But while they may lose a lot of settlers and workers, their military units are almost impervious to being killed by barbs. A lot of times I've found like 3-4 AI scouts or warriors just hunkered down around a lone barb archer or axe thrower, not fighting it, just letting it pummel them for dozens of turns so they can level up for free. They can do that because they get such a huge damage-reduction cheat against barb attacks, and they can heal up faster than the barb can kill them. Very frustrating to watch that crap. While your units would get killed in a jiffy, AI units just sit there and smile with 500 arrows sticking out of them, while they level up for free.
But since the beta, they are better about forming up hunter-killer teams to go eliminate nearby barb camps, than they were before.