It is easy to look at Kornak's Berserk, CC 22, DA close combat weapon and assume you are looking at a melee powerhouse and that isn't wrong, but Kornak has a number of deadly ranged options as well.
All profiles come standard with a Mk12, light flamethrower, and pistol. This gives him a good weapon at all ranges out to 24" and not terrible shots even further. Kornak also has several link options in the Morat Aggression forces that increase his effectiveness.
Kornak 3 armor and staggering 9 BTS assure that he can take a hit better than the average trooper, more so for special ammo like Breaker or Viral. He also has V: No Wound Incapacitation which will let him remain active after being wounded in many cases. PH 13 and Kinematika 1 also let him dodge very effectively, often a good choice from long range or dangerous weapons.
Because he is a Morat, Kornak ignores the effects of the Retreat, Loss of Lieutenant, and Isolated states. The latter means that he cannot be kicked out of a fire team by isolating him.
The combination of Beserk and DA CCW means that Kornak is very effective at destroying objectives in the missions that require it. He will have a 40% chance of automatically wounding it once and then also hitting with a PH 13.
It may seem like bringing Kornak as a decoy lieutenant is a good plan but remember that Strategos is not a voluntary skill so savvy players will know right away that he is not the Lt.
Kornak hates shock ammo as much as any other model with V:NWI. Due to his high PH mines are a less effective way to deliver it than usual however. Kornak will struggle against long range fire and camouflage modifiers. Also, it can be worth dropping a direct template weapon on Kornak because some players are tempted to use his flamer in return. Likewise, they may dodge leaving your own trooper safe from reprisal. You shouldn't have to dedicate too heavy of a weapon on him, but expecting a Spitfire to take him down if he is in cover and close range is not a good plan.
Don't try and take him out in Melee unless you really don't care about the attacker. It won't usually work out well for you.
Kornak is a good Lieutenant option for any Combined Army as his Strategos skill effectively grants you an additional order. In the Morat Aggression forces he suffers less from being an aggressive LT choice and can form a Harris with Sogarats, or Suryats (the latter of which can also include a Raktorak, Morat Sergeant Major in it.
Keeping Kornak hidden until he is ready to break skulls is critical. He will go down to long range shooters if caught out of cover. If in a Fireteam he will want to be placed safely because he will be easier to remove than the Suryats and may draw more fire. Once in a good range band he can do a lot of work with his Mk 12.
Active Turn Role
Kornak wants to hang back early game or move up under smoke cover with a Link. Later game he can out perform lower skill models, but in general he is a force multiplier rather than a power piece in himself. He grants you an extra order for the first few turns, then still has enough weapons and expertise to be an active turn threat later game.
While Kornak does have a light flamerthrower and Beserk, he is usually better off dodging. The use of either of the former weapons and abilities usually means he is taking a hit and you need to be certain the chance to do damage on the ARO is really worth it. Remember that Kornak has Kinematika which allows him to Engage at a longer range. This is a good option if it gets him into CC with an inferior opponent where the can shut down their attack run then destroy them in the active turn.