Carnage doesn't pick up until you have around 36 talent points, that way you can get Short Fuse and Enraged Slash from the Annihilation tree. Carnage itself really only starts to pick up speed when you get Massacre. My Marauder is level 36 right now and if he specs for Carnage, his Force Screams and Ravages will hurt after Gore is used, but he lacks some of the nice utility brought on by Annihilation's Force Charge talents, Obfuscate, Disruption talent, etc. Even the bleeds can generate extra rage. I find that leveling as Annihilation with the melee DPS companion set to have internal damage procs on her attacks makes taking down elites and bosses very easy.