Lower level priests and blood sacrifices.

[Graeme Dice]

Ighalli said:
But Mictlan also has to buy temples. So now, instead of having a slightly more difficult time spreading dominion and getting a much more efficient effect, they get no advantage (unless they can do multiple slaves a turn) for a priest and a sacrifice each turn. What level are all the priests they can recruit now?

Requiring blood slaves for dominion spread is likely supposed to be an overall disadvantage, not the advantage for Mictlan that it was in Dom2. This is a balancing factor against their extremely efficient blood slave hunting and having mages that can easily cast the majority of the powerful blood spells.