[DrPraetorious]

I don't think that the fire vuln makes much of a difference.

Five of Amos' blood knights cost 700 gold and 190 resources. That's the same amount of gold as thirty five longbowmen and seven wardens of avalon - who can, likewise, wade through indie provinces without losses. However, those mannish units cost ~450 resources, the vampires are much easier to mass.

The real issue with recruitable vampires is the same problem I ran into with my various tries at well-equipped goblin nations. Goblins have essentially a human statline, and pay only size 1 resource costs. It's vicious.

Vampires are essentially giants (better, in many ways) and pay size 2 resource costs. Vicious.

So, there are a couple of ways to resolve this:
* Naked vampires can have a base resource cost (a large one.) As there are no recruitable vampires in the basic game, this is not a conflict with basic game expectations (if you care about this sort of thing.)
* Vampires can have #ressize 4. You could say that they demand the finest armaments, but this is non-conforming (I don't believe that any other unit does this.)
* You can make special armor and weapons for the vampire units and just set the resource cost ridiculously high. Armor them in blood metal, whatever.

Anyway, at prot 17-20, with that statline, they should cost > 75 resources *each*. Try that and see how it works out for you - for one thing, you need to take productivity which severely limits the efficacy of your blessing.