The damage is low because it is doesn't have a very fast rate of fire. Technically, the Pulse Rifle is also not that strong either, but due to having a faster fire rate and the ability to burst fire (which burns through ammo like a pig who quit its diet), it feels like a stronger weapon.
As I said several times before, I'd think upping the damage just a pinch would make up for the low ammo cap and average RoF, allowing the marines the option of a fast shooting, low damage weapon, or a more damaging weapon that rewards good aim and tracking instead of mindless spraying towards a target.
Also, if you play as a PFC, getting extended carbine mags from your PFC vendor only costs 10 points a pop, meaning you could get upwards of 4 35 round magazines to satisfy your ammo needs. The carbine also uses the same ammo as the Pulse Rifle, which means that you can take bullets from Rifle magazines and transfer the ammo to carbine magazines if you really need to.