Why whould you ever choose Mictlan?

[Huzurdaddi]

but that is payed for through the relative troop weakness of the theme

I would say that head-to-head the Blood of Humans theme has much better troops than Mictlan.

Mictlan has good magical diversity, to my mind excellent sacred troops, and the best combined economic/research/blood ramp-up in the game. what's not to love? (other than their early game crap dominion)

Mictlan has plentiful scared troops I do not know if I would call them excellent.

Don't forget that the magical diversity of Mictlan has a couple of limitations: all of those wonderful casters are capital only and they have no randoms at all. That is a pretty heavy price.

Mictlan's negatives are that their troops are very fragile to missle fire, their excellent ( but costly ) casters are capital only, and their dominion costs an additional resource ( this also has the side effect of making their micromanagement quite difficult ).

To compensate for these negatives they get the best blood hunter in the game ( by a percentage which I think has been painfully calculated by now ), the ability to take both the magic and order scales, and the excellent, terrific, awesome Tribal king.