Mythic Sarkareth was actually massively nerfed on the Weekly reset, being nerfed much more than intended due to a possibly unintentional 33% nerf to Oblivion damage. Good luck Hall of Fame pushers!
While yesterday’s hotfix notes and spell data indicated that Mythic Sarkareth had a 10% nerf to Oblivion damage, it appears from logs that damage per stack of Oblivion on Mythic has been reduced by a massive 33%, from 15,830 to 10,619.