The common complaint about Kullervo is that his 2 stinks -- it's his primary method of survival, but overguard is simply terrible on a frame with no shield gating (setting aside the paltry 5k cap).

To fix him, just replace his 2 with gloom, which is great for a melee frame. And getting rid of overguard means you can benefit immensely from [Hunter Adrenaline] (which will give you plenty of energy for Gloom and spamming the rest of his kit) and Arcane Grace, much like the other two shield-less frames.

He's great with any melee that has a fun heavy ability, but especially the Incarnon ones. I especially recommend Hate Incarnon Genesis, which removes the need to even equip guns -- you can just spam spectral scythes instead.

I recommend Naramon for focus school. For Archon shards, either Azure for armor or Crimson for melee cc.