Some of the other frigates are carriers, while the Arquitens-class is a light cruiser designed to escort other ships (such as freighters or carriers). Compared to other cruisers, the Arquitens-class is small at 326 meters long, though similar ships include the Hammerhead-class cruiser and Kaloth BattleCruiser at 315 and 307 meters, respectively. These three cruisers are similar in length and cargo capacity, though the Arquitens-class can carry the least - but it is also the fastest. You could likely argue that cargo capacity was sacrificed for the more powerful engines.
You could also look at the fact that it was a CP ship, which are usually implemented as weaker than produced entities for game balance.