Dark Citadel Greater Cosmetic Drop Rates?

I have done so many Dark Citadel runs and I only have gotten 1 drop of the greater gear set aka the glowing one. How rare are these? Does anyone have any good farming methods besides spamming the final boss wing over and over again? For reference I have done enough runs to get over 40k citadel coins and only have 1 of the 5 pieces. That rate seems insanely low. I get blizzard not wanting to give away cool cosmetics easily and to make them rare but this seems dreadful and I haven't seen them address it anywhere yet. I at least wish we could just buy them from the vendor for like 20k a piece like the weapons as a way to combat bad rng. That would still take hundreds of runs to get enough to buy the set.