Jutrea, the thing about the Mictlan sacreds is you have to think of them much more like a brightly burning flame...they're not meant to last. No matter what you do, at the end of the day they're low protection without all that many hit points. The best defense is a good offense. Going with a earth bless is just cross purpose, and doesn't really buy you much. They don't have much encumbrance so the reinvig doesn't really help, and you're not really making a significant difference in their protection. I actually find that the astral bless is surprisingly effective at improving their staying power. The first hit is negated by the blessing, and at least one other hit is negated by the shape shifting, so you end up having to hit them many times to take them down (not easy if they've also got a water bless)...while they're wailing away at you with a huge sword quick sword.
Plus, as I mention there are some other real good reasons to take astral.