In short, having higher "defense" and "skill damage reduction" will decrease incoming damage from enemy's "Skill Amplication".

However, no matter how much "defense" point you have, it will not protect you from enemy's "extra skill damage" ("extra skill damage" is something like true damage or flat damage). What protect you from "extra skill damage" is "skill damage reduction". Checkt the formula at [url=https://eternalreturn.fandom.com/wiki/Formulas]https://eternalreturn.fandom.com/wiki/Formula