Are devils worth 7 blood each?

[Cohen]

I'd agree with Boron ... he's a good analyzer.

Abysya is very rushable. And is totally defenceless except a good pretender. Aby infantry costs a lot of gold and resources and you can't pour out many of them.
You probably start recruiting Warlock type mages that are good at research but are useless in combat at early stage (and mostly in late unless you use blood magic ... please make sure in the next patch slaves don't take fire by heat aura).
I add the consideration that Aby infantry, for how much it could be strong, has a very bad morale for his cost, and thus is too weak at capturing indeps or defending. Unless you want to afford a 360 gold mage that is a pretty useless battery (due to poor aim) and that could cast fanaticism, depriving you of many gold AND a mage that can research (this is very bad for Abysya due to bloodhunters and researchers capitol only).

I've already made my proposals in previous Posts.

EDIT: About Vampires the cost isn't for Summoning Allies, but for the presence itself of vampires, so you're losing X pop for every single vampire you've, and every turn.