The only relevant information I could find is this post which says:
For normal attacks against an enemy with 0 DEF:
Base = (Attack_Stat(s) / 3) * (1 + Crit_Chance + Combo_Bonus) * Position * Class_Bonus
DMG = Base * [1.00 ~ 1.20 in 0.01 increments]
Attack_Stats(s) refers to the mean of stats connected to abilities/weapons. I do not know what
Combo_Bonus are numerically. This is also ignoring defence, which is the main reason I want to find the formula.
From reading various threads it seems given a fixed attacker strength there is an amount of defence where you will take zero damage. I only mention this because some games have minimum damage or diminishing returns on defence.