This is to do with how stats work in this game:
How do each of the stats work (More specifically, the combat stats, because it seems like all the skill scale off of Attributes)?
Also, this is gameplay wise, and tested by myself, but I don't think making DEFENSE a straight damage reduction is good. Usually it should be percentage reduction, not a straight unbreaking armor type. To give context, one of my skills can deal 849 damage. If the enemy has 18 DEF, I deal 18 less damage. If the enemy has 1000 DEF, their DEF will completely negate my damage, and make it 1. That's not how defense usually works in games... maybe you could make DEF as scaling damage reduction, that interacts with the combat stats of the character (like say, ATK). Additionally, this might just be me but I dont see CRITS happening in the combat log, even with a 55% CRIT rate...
I recommend maybe taking a look at this website for inspiration on how DEF could work in combat: Damage formulas.
Additionally, this is how I think damage in combat could work:
Final Damage=DMG Dealt by Skill ×(ATK/(ATK+Enemy DEF))