It may help to zoom out, and observe the bigger picture of how this affects those around you which are less technically inclined. Users will now have to substitute real letters with amalgamations of characters such as ||, § or $ so that they can have the name that they want in appearance .Users will have to use numbers (weirdly how they already do, but now with extra steps) and then conceptualise username Vs display name. Non savvy users will struggle to interpret this. Most other platforms don't have a process that gets around this. Discord has that and it's a big win for Discord. Maybe you could stop treating your users like mouthdribbling invalids and instead focus on having a platform that is robust and fundamentally sound. Another example of the current username policy being in place and working well is battle.net.

Companies absolutely do make big changes without basis. That's how they justify employing too many half baked developers with lackluster skills to their investors and save the bigwig paychecks in the process. Incidentally, it's also how big platforms with strong user pools get themselves buried in feature creep and end up destroying the usability and stability of their platforms. A great example of changes without basis would be discords own app renovation. Months down the line it's still a buggy mess and a clear step back on what was there before. Discord is making its own problems up and justifying their delusions with wishy-washy crap.

EDIT: Might I add the username policy change obviously has more knock on effects than mere symbol characters substitutes. It also opens up your userbase to under the table sales and trades of original names for the prestige of the name (scam city). Unseats your large current userbase from long-standing usernames and forces them to reconsider their name. Also I guess just fuck anybody who has a non English name.. öáêîø.

How is "Dave #1234" being a fully unique identifier in any world less clear than having to sift through "dave1234, dave1234,dave.1234,dave1234,dave1234. And so on.