^Edit:
I did some searching out of curiosity and it appears that it only works with weapon damage. Here’s a reference to Essence of Ch’thon, which is essentially the same effect.
Sorry if this has already been posted in this thread(didn’t find it), can someone please explain how %chances on augments work?
Example 1: Essence of Ch’thon(weapon augment, %chance to reduce resistances): does it need a skill with %weapon damage(and scales with that) or is it also useable by casters not using any skills with %weapon damage? And is it a %chance on attack?
Example 2: Kymon’s Will(jewelry augment, %chance to lower enemies damage): same questions, is it a %chance when hit or on attack? If its when being hit, I assume it works for every character, but if its also on attack, again, does it need %weapon damage or not?
The way that Grim Dawn works is that every proc happens on attack with weapon damage % unless otherwise stated. In your first example, resistances will only be reduced if your attack has % weapon damage. That means it won’t work with skills like Trozan’s. Some skills without a weapon damage component can reduce resistances, but they will explicitly state that they do in their tooltip (like Curse of Frailty, Agonizing Flames, etc). Your second example follows the same rule: it only works when you attack with weapon damage %. Some effects do indeed activate when you are attacked, but they will explicitly state that this is the case.
So in this AAR caster it is probably not useful considering it would then scale with %wd, of which there is 20%WD (via Guardian’s gaze) = 3% effect. A movement rune with 100+%WD might make some use of it.