If the username "chilidogdude" is highly sought after just anyone can have that username but everyone has to have a discriminator added to the end. All users are equal, and it also means no one can get a username that's exclusive and then try to sell it.
Usernames are only to establish chats anyway, after that you don't see them so it's not that big a deal. 

 Hmm 🤔! Understood! Telegram usernames are actively bought and sold as NFTs 

 Well, some discriminators are more sought after than others. In the Bitcoin world that would be 21, so they can still be sold, for example on @Plebeian Market 😉