Kind of weird that someone who focuses solely on battle would have a lower combat power.
He focuses solely on battling in short range with weapons, so his combat power isn't inflated by things like magic, stealth and other abilities.
People like Viro (or Willow, depending on the translation) and Sera, or even Aria herself function as solo fighters, so their ranges of skills are wider than those of someone who operates in a party in a specialized role. Therefore, this guy's numerical score on combat power is comparatively lower.
That doesn't necessarily mean he's outright weaker, but he's certainly less versatile and more dependent on his party members. And he's just lost two of said party members, and the third one is injured.