Zos's new chapters are such garbage these days that their only selling points are putting in a must have Mythic item. Zos knows these Mythcs are over powered but also know that people will be desperate to have them.
Once the sales grind to a halt they nerf the Mythic to what they originally intended it to be. Not much to expect from a company that allows a Dev to call it's playerbase "whiney little b*****s"