For everyone's reference, I have now completely redone the monster health numbers. They are now MUCH more accurate, and for about 80% of the bestiary, quite accurately represent the creature's histia (±10% due to monster variance).
Note that, on average, 10 Darkus do 1 histia worth of damage (±0.5 histia due to darkus variance). Note that most races start with some Darkus, so you will do a bit more damage than you expect from trained darkus alone.
This means a fighter with ~450 Darkus will have a 50% chance to one-hit a monster with 50 histia, like a Dust Arachne or a Bolok Cougar. This same fighter will take, on average, 2 hits to kill a Vagrant Arachne, and more like a whopping 22 hits to kill a Darshak Corsair (commonly found on the west sea entrance to Tenebrion's Island).
I have gone through personally estimating about 80% of the creatures in the lands, but a few areas I have estimated and may still be quite off:
Ash City
Estuary
Metz (anything past jungle)
Glen (myrm and wurms)
Ethereal Plane (have about 50%, but then a greater death spawned in portal island)
Deep Orga (anything in Orga CIty)
Exotic Locales (Turmoil Plane, Astrum Crypt, Lugubrion's Keep, etc)
Rare monsters (Juliosaur, Puma, Albino Maha, Mantuan...)
In time I will update these. Estuary, Glen, and EP are the easiest, the rest might take some time. I'll probably tackle monster Darkus afterwards. I still think my numbers on "atkus required to hit" and "defense required to brick monster" are pretty good, but please tell me where I have errors. At present, Estuary has, by far, the most inaccuracies.