As the Vanheim player Psycho referred to above I'll mention that I had a dominion of 7. Obviously not high enough that I was planning on a dominion kill victory but of course I intended it to be a tool - especially in the MA where there's only one other blood sac nation. My initial worry was actually MA C'tis and I did in fact start next to him and he did have a crazy strong dominion (if I didn't know better I'd swear it went to 11). When the province south of my cap switched to his dominion I decided it was time to started blood sacrificing earlier than planned.
Then when I saw Pan's horde of vampire lords (and that damn VQ) it became even more important. Interesting to hear how many dryads he had preaching because I was surprised when the blood sacrificing eventually failed to convert even some of the provinces where I had forts and was sacrificing. But certainly what finished me off was the destruction of my blood economy. Another thing that I think limited my sacrificing is that I had a string of provinces leading up to and through Pan's territory - I would preferred to have been able to face him with a solid block of provinces with my dominion maxed out.
Funny side note from that game is that I couldn't protect all my provinces from his raiding so I'd choose a few each turn to send anti-thug squads to. And I would almost always guess wrong. It got to the point where I didn't try to figure out where he would attack, I'd just randomly select provinces to defend. And I'd *still* be wrong. I still have a strong hatred of Rock the golem.
Not sure if blood sac is OP but barring a patch changing the mechanics it seems a possible fix is removing jade knives or making them more expensive.