The mythic ring is from the previous lvl cap, meaning it is competive for best against top legendary gear.
As I said before, it is likely an error to be epic and is meant to be a hard to find legendary item. I imagine sts will change all current ones into legendary & start making them drop as they were intended.

If these became legendary, things fall into place with the mythic rings. These offer more damage, while mythic rings offer greater survivability.


Also...CHILL, GUYS!
Sts seems to be working on things every day of the week and constantly trying to adjust the game to create a great level of balance in things while adding new content. They are constantly coding lots of things. Sometimes a small slip up happens in coding and big effects result. But at least they acknowledge the mistakes and fix them as quickly as possible.