For Algaloth in particular you spend most of the fight (depending on positioning) attacking from the front so you will lose some dps. You will also lose dps in the felfire phase whereas other classes will have dots, poisons or can continue to use ranged dps.
You can try moving slowly around the boss's hitbox in felfire phase, but if your raid as a whole are doing 10k+ it's probably best to concentrate on avoiding dmg. Personally I think your dmg output is about right for your gear and where warriors are right now (pre patch 4.06)
Hunters, rogues and locks are PURE dps classes, Blizzard intends for them to out dps you. You lose a little dps in exchange for the flexibility of fulfilling either a dps or tank role. In addition, you are taking time out of the optimal rotation to add sunders (which I see you have glyphed to colossus smash), this might lose you some personal dps but will help the raid as a whole and is a GOOD THING.
I think it's time for Warriors to stop feeling bad if we're not number one on dps - we're not in Kansas *cough* ...Wrath anymore.