Like i said earlier, SE usually always adds drop rate buff (if any) in the patch notes. I have read every single patch note and keep a binder with all of them as reference and Nightmare was never increased, the name is fitting i guess, lol. Farmed the crap out of Primals back in the day, helped a friend's friend last weekend as they needed all ponies and nightmare dropped 2X, got it
I do agree it should remain as is though