Same thing happened to me. I had ton of challenge with the first few bosses of the vanilla game, then I entered the chalice dungeons and at some point the blood echoes reward becomes just too high for the difficulty. You end up overleveled and everything else in the game, including the DLC, is completely trivial. I oneshoted everything in the DLC except the last boss at lvl 90-100 just like you. I could just tank the bosses and chug vials without any sort of skill.
The number of blood echoes you receive in chalice dungeons depths 3 or 4 is just too high considering the difficulty of the ennemies.
The number of blood echoes you receive in chalice dungeons depths 3 or 4 is just too high considering the difficulty of the ennemies.