Well, I'm not AN(obviously
) but I imagine that their fanaticism may be acting like a (potentially)cheaper offensive form of kicking. That would help them do all this, and would explain his comments about them running hot and overdrawing. Further from that, the Harmurri might have been weak militarily since they were expecting us to protect them, and the khem colonies they took were mostly empty I would imagine.
Additionally, we don't know what military innovations they have had but we simply haven't noticed considering their isolation and intrigue skills.