AI players seem to have great difficulties coping with barbarians. In my current game (monarch, world of erebus, epic speed) first civ kicked the bucket around turn 150, Lurchuip followed on around turn 300 and Lanun soon after that. Okay, it might be that other players got them but somehow I highly doubt that.
What I can with certainty report is the performance of my neighbour. At first she seemed to handle this okay, and built her second city around turn 150. She lost it to savages about a hundred turns later. I didn't bother to go take it because I hoped she could retake it but she couldn't.
On turn 360 I finally went to take her out of her misery and found her holed up in her capital with 5 swordsmen. Surrounded by 2 barb javelinthrowers on one side and one barb dwarf sling thrower on the other side. Sling throwers age was 130 and both javelinthrowers had also ages 100+. All of them had at least +80% str and ranged attacked the city every turn. While still fortifying on forested hills around the city.
It took me lot more effort to clear the barbs with skeletons, ritualists and Rosier than to take the city itself...