[Cohen]

Random attack on Soul Contract bearers works!
I can assure, at least in 2.12 ... where I didn't known that Soul Contracts attracted horrors and assigned them to Warlocks and such ...
I'd agree in fact that only Blood Mages could get the Soul Contract.

Warlock:"Hey Scout, come there, I've sold your soul to Hell Lord"
Scout: "A well, what I've gained? Eternal Life? Neverending youth? All the women I want? To become the richest of the world?"
Warlock:"Oh yes everything of this ... put a sign on those contract"
Scout: "Wow" ... and signs
Here the first Devil appears but the Scout can't issue him any order and the Devil start rampaging for all the countryside in a frenzy killakilla.
Scout: "Mmmm there should be something wrong in that ... unless that red stuff is my first female"



About Fallen Angels, nothing to say to they Summon Allied Imps ... since Imps are good only as sieging and defending force (don't eat, and fly). Even Fallen Angel itself is far weaker than an ID for his Blood Slave cost (I know he's more magic, but why it is far less used? Probably because it's too weak even if it is not unique).

About Vamps, I'd agree to remove them the Summon Allies skill. They can easily cast the vampire summoning spell.
Otherwise may I suggest a rule that a Vampire in a province feeds himself with X population at turn (1 to 10), I mean Vampire, Lords, Count, Queen or whatever.
If the Vampire in question doesn't find any suitable pop victim, he'll dissanguate 1 troop non lifeless non undead non magical of your army (note: Commanders won't get touched by Vampires). If there're no living soldiers the Vampires that aren't fed should become an indipendant force proclaming a vampire a vampire commander (perhaps upgrading to count) and revolting against the army they're in, or they simply migrates in the next friendly owned province to seek new feeding.
This could prevent you to keep vampires in your land, going to attack forcefully unless you want to see your lands get depopulated as an Ermorian province. And usually to go in enemy land you'll need a strong dominion at least ... well not so difficult to reach with Aby or Mic that can sacrifice however, but however they eat pop of provinces that are going to become yours.
If Vamps goes hiding and eat in enemy provinces, a message like the unrest caused by spies should appear.
Solar Brillance spell should be mostly effective too against Vamps, killing them asap it is cast in battle.
The Second Sun global could burn them out too. (beware all ppl will be interested in dispelling it or attaking you because their provinces will get warmer)

If you have to issue an order to produce gems, even for a better alchemize, you probably have too many mages spending time creating gems, making this strategy totally wothless considering you strip resources to your research and combat firepower.