I'm inclined to think that they sound a bit on the overpowered side- also, it sounds like they had only been involved in a single space war, so how they could go from that to being able to exterminate a civilization while the other galactic civilizations just watched is totally beyond me. Some other factions would have told them to back down- you don't wipe out a civilization because one cargo ship got attacked. After all, if they were willing to do that, then every galactic civilization would be at risk, since all it would take is one pirate crew attacking one ship and suddenly their entire species is trying to exterminate yours.

If they were that quick to rise to that level of violence, there is no way they wouldn't be involved in an ongoing war with every other spacefaring race.