[2023] Original Sin stacking with resist reduction

I'm working on a poison spark build that is now incorporating Original Sin into it. I see on poe.ninja that 33% of people with Original Sin are also using Despair. PoB also shows that casting Despair and having Void Beacon on Occultist are large DPS increases, even while wearing an Original Sin.

It's my understanding that having an "is x" modifier like Original Sin overrides any other sources of "enemies have -x% resist". Am I incorrect or are 33% of Original Sin people and PoB incorrect? I assumed it works exactly the same as Doryani's Prototype, which prevents the use of "enemies have -x% lightning resist" because it overrides it.