discord is most likely well-aware of the criticism that it's an unsearchable black-hole and that people are nonetheless bashing it into being a docs/wiki system despite the poor product fit.
when your customers start doing weird shit with your product, they're telling you what they want the product to be, and as a result discord is pivoting towards being a forum or at least having the option for communities to have public wikis/forums associated with them.
this is probably only intensified now that reddit is teetering in the middle of their own pivot and leaving this opening for low-friction community building. like why not have a reddit replacement for the public content, built on top of the discord communities that already exist?
but, reddit with non-unique usernames would kinda suck, wouldn't it? to make a global public forum work, you have to require that they're unique and migrate the existing usernames to the new schema somehow.
You don't have to use the new username, discord's legacy functionality isn't forcing you, but if you don't you probably won't get access to disreddit features when it launches, because replying to paulmd#0069 on a reddit-clone would be an awful experience.
but the reason the username change is happening "even though nobody asked for it" is very simple. nobody is asking for username changes, but lots of people are asking for discord to step into the gap that reddit is leaving, and provide more powerful public-facing tooling for non-ephemeral content that's searchable and discoverable. And unique usernames are kind of a mandatory part of that model.
I haven't really used Lemmy/Mastodon much but it seems like an inherent disadvantage of that model too. weedgoku69@mastodon.social is not the same user as weedgoku69@masty.me and people will have to get used to the idea of looking at the whole username rather than reddit's unique usernames.
It's also going to be tough when there's not a 1:1 correspondence between "subreddits" and the discords underneath them. I guess your discord.gg URL is now your canonical subreddit URL... hope you boosted your server and squatted that custom invite URL a couple years ago, because it's your "domain name" now!
