120% weaken is easy. 90% + 30%. Also weaken gives almost ×2 more DMG than without from what I've tested and even on the strongest of enemies, it makes sure your DMG doesn't get divided by below 1 from resisting enemies. When weaken is above 100%, it will always proc and it's a Debuff that could be applied universally to hirling Like the ascendant Debuff. Weaken + ascendant is OP after all.
Ignore resist is fine because it makes all enemies not divide your DMG below 1 but you won't have the benefit of dealing ×2 nominal DMG that weaken does. Weaken is vastly better and even kills immunity enemies easily by nullifying it.
I remember when Ignore resist was the Go to affix but those days are not as relevant anymore since you have weaken way over 100% with ease , ascendant Debuff, the weaken probably applies universally like ascendant + wrath talent.
Before weaken crystal affix was 90% and cap was 200%, weaken used to be 60% cap and 45% crystal affix so at that time it wasn't worth it, even though ascendant did help. However when weaken got vastly buffed to 200% cap, 90% weaken + 30% epic affix, weaken suddenly becomes relevant since it kept pricing so much , the insane DMG gains , etc.