Besides that, you get a free +1 boost to tenebrium weapons for all chars and a skill book for another free bonus to one character, meaning that spending more than 6 skill points seems absolutely unnecessary anyway.
But the bonus from Tenebrium still increases for every point past 5. With the +2 that you get from the quest / book you can get another +3 from gear (Legendaries only), since Tenebrium can be boosted by rings and amulets while the other weapon skills can only be increase by +2 from belts and bracers. So with leadership you will end up with a passive +115% damage bonus compared to the +85% that you get from regular weapons.
