I’ve been always curious of that, why there’s only skill level bonus for Ravenous Earth, but no modifiers at all? If Blightlord is the intended set for vitality RE, how about give Dark One another skill’s modifier on Necromancer’s side?
decent/strong support utility perhaps for a dark one ritualist/cabalist 
- while not wanting to buff it to be a main attraction
Dark One RE/totem Ritualist as example is a nice starter char [1.1.8.1 - 1.1.9.6] Dark One's Reborn: Vitality Caster Ritualist ( 4:30m Crucible, 5:33 Naked Ex, SR 100, Ravager of Flesh, Crate, Callagadra, Mogdrogen), but you then have the option upgrading it into stronger endgame mode later
Unsure if there is/would be a comparable decent support skill for Rit/Cabbys, but i don’t think blightlord would necessitate removing the skill support, even sans modifier, as the utility is much different.
(siphon souls wouldn’t feel as great on bosses during levelling etc)
Because Vitality RE is traditionally overlooked/undersupported by devs for some weird reason. Right now skill itself is not very good but that’s a different topic. I agree that Dark One having some flat damage/flat cd to RE wouldn’t hurt at all or make it op.