I played some arena matches in a 3v1 AI match and won. Magic armor and Physical Armor were depleted really early in the fight.
I had a warrior, ranger and mage vs a combination of 9 rogues,rangers,warrior's and mages.
The AI seemed to keep attacking me with Fire spells on my warrior while he was blessed which kept healing him under the formula that the fired turned to Holy fire and healed him. So armor aside I think blessed might be what to look into also.
I think it is nice that you can't guarantee CC on the first turn with the armor system, I think further on you will be able to better heal armors. Some abilities like Oil ignores armors. To me, it just adds to the tactical system.
Much like if a static cloud or an electrified puddle disappears after one person walks in and gets stunned now.
Or the AI will look for a way around fire if it can, the key point is if it can.
It would be interesting to test this out on a tactician or honor mode setting where they will have 20% better stats if the same as original sin.
