Kalastor and Drain Essence are pure Acid, Sigil was already 66% acid and the flat vit on the set bonus was changed to acid. It’s an acid set.
The % vit is there because items have the % damage that is being converted into the actual damage type of the set (Deathmarked has % pierce but the set has a bunch of conversions from pierce to cold). The elemental to vitality doesn’t make any sense for the set anymore, but it doesn’t do any harm to keep because of the skill mod conversions.
I’m more upset with why Sigil lost the 1,5 secs cdr and the 50% energy cost reduction mods.