Actually tenebrium weapons are worth it, because they have a crapton of damage even without sharpening. And correct me if I'm wrong, most creatures in the game have no tenebrium resistance and receive the full tenebrium damage, unlike elemental damage.
Resistance or lack thereof is definitely an advantage. And yeah, the damage is nice even without sharping, but as I said, if you add elemental damage and sharpening than the tenebrium weapon does not look that good anymore.
That the tenebrium skill works above level 5 is new to me, might give them a small overall edge than I guess.
