Discord's Recent Announcement made a lot of people mad, mostly because of Hyrum's Law - users were relying on unintended observable behavior in the original username system, and are mad that their use-cases are being broken despite very good evidence that the current system is problematic. I think the major issue here is that Discord didn't go far enough, and as a result, it's confusing users who are unaware of the technical and practical reasons for the username change, or what a username is even for.