The difference in affordances between "everyone has a number attached" and "somebody who isn't you doesn't" should be obvious.

My username on Discord is "Ed#1234". My username will not be "@Ed". That sucks, the change isn't my choice, and I've canceled my subscription because they're removing the one feature, as much of a vanity thing as it is, that I liked enough to give them money.

(This isn't an invitation to well-actually-that's-illogical about it. I could not care in the slightest if you think it is sufficiently lesswrongish to be valid. They're changing my username out from under me. That sucks. They have lost me as a customer.)

if I have a unique username in the form of a name + a 4 digit number, why do I need to create a unique username? The logic behind this doesn't make any sense other than the fact that they want to charge for a blue checkmark and/or they aren't satisfied with their current username setup. Both of which are not my concern as a user of their product. I shouldn't have to win the lottery to get my username back. I shouldn't be outbid by some kid with a python script who wants my name. Your name is your only true property on 3rd party sites/services. My username, is me. I am my username. To change it would be to change me. I kinda like me.