Interesting, would never have guessed that. Thanks for the tip.
I really need to start looking at actual values instead of simply looking at (de)buff icons to tell what takes priority/is most efficient >_<. Based on the numbers you provided I'm assuming dark resist down is part of the 50% cap? That's..... odd to me, unless the normal defense down cap is 40% + 10% cap for elemental resist down. If the generic attack/def debuff cap is 50% though (which includes elemental resist down, atk or def), that just seems like a really bizarre way to go. Not saying you're wrong mind you, just seems odd to me.
Anyway thanks for the super helpful info Aidoru and Slashley as always (including parts not added in quotes for brevity)!