Based on many rather lively conversations and complaints concerning this skill, I've come up with an idea to tone deathblow. If I have understood correctly, The deathblow that hits the opponent causes 2, 3 or 5 times the normal damage of the blow. My suggestion was to combine deathblow with the number of PC opponents that are fighting the berserker.

1 PC opponent: Deathblow does 2 or 3 times the normal damage.
2 PC opponents: Deathblow does 2,3 or 5 times the normal damage.
3 or 4 PC opponents Deathblow does 2,3,5 or 7(or alternatively 6) times the normal damage.

The PC opponent is seen as a PC directly fighting the berserker.

Now, some motivational part on consequences:

-Berserkers are meant to be brave. Deathblow as I suggested it would favour berserkers that attack groups to get that mage killed.

-Berserkers who take the front in raids are toned up by this change.

-Berserkers who deal deathblows from the back row are toned down by this change.

I know I don't really have experience with playing berserkers, but Imms can tell if the idea is good or not. Feel free to give your thoughts on my suggestions. If you (dis)agree with me, do tell the reasons why. If I am working under false assumption concerning the current deathblow, feel free to correct me so that the toned version can be adjusted accordingly.