Ok one thing why blood dies alot they have no resistance to magic. Hense theres the unholy portion anti magic bubble. Thats right there is a life saver stay in your bubble and they come to you and its melee spread disease die. Also with unholy yes you get a ghoul so with two you send ghouls in on a target while they focus on them you pull one guy at a time its easier then getting beat on. Second with unholy not a big deal but increased speed running places. Two your diseases do way more damage then just blood. Oh biggest thing anti magic bubble two min cooldown so thats why i have two. One puts up bubble fight one group move next puts up bubble fight. By the the time two fights are done your first guys cd is up. So thats why i have two so i never have to worry about casters and not having that bubble because cutting 75 percent spell damage for 20 secs is nice or i think its 12300 damage. I hope this helps answer your question.
Submitted for your approval lol.