I suggest doing a quick search of the spell, it was a main warlock thing. “Mana Tap”.
The name may change (syphon, drain, tap or what ever) but the mechanic still the same, mage / warlock / wizard taking mana from a living being.
Yes it was the first racial of the blood elves in WoW, but at the same time it was a core spell of many “classes” and “characters”, Kael had the tittle / class “Blood Mage”, and he did drain mana, same goes for the Spell breakers. All that inspired the racial for the WoW BC counter part.
And yet every warlock has it. Gul’dan had it… so it is not a “racial” lore wise, is jus something learned to feed their so called addiction