Rogue Necromancy is a hefty chunk of soulstones to be spending, considering you're reducing it to half wounds - would you then hold it back and heal it up in order to make it last longer, or do you try and get as many turns as possible out of it?
I've seen the kind of damage the Coryphee duet or a firing line of guild guard can do, and I'm not sure I could justify spending a third or more of my gangs soulstone allowance on the necrotic monster when I still want my Seishin wall and the Shikome. (along with the Hanged, Lost Love, and that, and that, and that...)
I still need to figure what I'm running with Kirai though, so what do I know