Agreed but not certain on what the rate should be. 1/50 sounds fairly reasonable but possibly a little too common as brimstone keys are mostly a bi-product of training slayer/magic etc. I've personally used over 450 keys without a single piece obtained over 200m normie slayer exp - 18m realism exp - 13m+ leagues exp
Collection log for dusk items is way too hard here, knowing the brimstone key drop rate and the drop rate of dusk item from chest. I am very supporting this idea!