The lack of tanks in the Necropolis faction is noticeable because if you teleport a Hydra or Golem into the neat rows of your army, you can't ignore them. You'll be forced to fight them, and there's no one in the Necropolis to send forward to attack the enemy's mages or archers; sending only Vampires forward means they'll be lost, and Spirits probably won't help either.
The lack of tanks in the Necropolis faction is noticeable because if you teleport a Hydra or Golem into the neat rows of your army, you can't ignore them. You'll be forced to fight them, and there's no one in the Necropolis to send forward to attack the enemy's mages or archers; sending only Vampires forward means they'll be lost, and Spirits probably won't help either.