The majority of Tenebrium weapons I'm seeing are crossbows, which I'm assuming don't benefit from the crossbow skill, therefore making them pointless because they have no crit chance and take more AP than normal bows to use.
Also, I'm seeing a lot of enemies with 100%+ Tenebrium Resistance, and I'd rather not have a weapon that can't deal damage to certain enemies at all.
I find that having Crafting at level 5 and just adding Tenebrium damage to existing weapons benefits me more.