As a Marauder who has tried all three specs, they all work. Rage works really well when clearing trash on the way to a boss. It doesn't work as well as Carnage in boss fights, but the damage is definitely still there.
I haven't tried Annihilation in a HM or OP since I hit 50, but I am willing to give it another go.
Carnage is really ****** spec for boss fights. The damage is consistent and when you get Gore up and then use Force Scream, it hits pretty hard.
All-in-all. As a marauder, I would feel comfortable in any spec in an operations group. You just have to be on your game when it comes to getting out from cleaves and AEs. Don't make it more difficult on the healer.
You are doing something wrong. I have 1 Rakata daily piece, and full Columi. I hit from 3.6-4.3k. Are you putting Force Crush or Force Choking the full 4 stacks of the buff before you use Smash? If not, that would explain the low amount of damage.