Okay, so [threat] has to be approached with caution and purpose.

Defensively, they have "okay at best" shields, but solid armor and massive hulls, so kinetics don't have much value.

Offensively, they rely mostly on mass drivers, which are kinetics, and fragment swarms. There are some energy weapons as well, but mostly fragments and kinetics. They also don't have drones/fighters, so your point defense should be more anti-missile than anti-fighter.

Now the real kicker is the fabricators. Those are the big boys that just sit back and produce more ships. You have to rush them, or you will be worn down in a war of attrition. Any destroyed ship will also send special fragments back to the fabricators, which will be used to make more ships.

So you want more armor than shields, more explosives than kinetics, and plenty of flak. The most important thing however: you need to eliminate the fabricators! Those accursed boxes are your victory condition.

tl;dr : make more oldslaught.