It will get 30% damage per debuff. In normal ocasions, you’ll probably inflict Crown, Skull Swing (gives another adtional damage, but undisclosed) and maybe Bleed.
That’s 2 or 3 constant debuffs, representing 1.7 or 2.2 times more damage.
But now, consider those heavily debuffed World Bosses, with, some times 9 or more debuffs inflicted - that’s a 10x damage multiplier.
Now let’s say that you have 800 PATK and the skill at lv5: the damage dealt to those bosses would be 25000 minimum (we don’t know what is the Skull Swing buff modifier).
Is it worth it? Idk, maybe yes, maybe no.
We have to test.