Oh, I wasn't really commenting on an imbalance, I just couldn't resist answering your question on who could push a blood sacrifice in MA as I'd recently don't that myself.
I will say I play blood nations a lot (often with high dominion) and I've never seen anyone move dominion half as fast as when I start dumping blood slaves into that. As I mention though, haven't been in a dominion victory game so I don't really have an opinion on if that's unbalanced.