it’s first come, first serve for unique domains. but for requesting aliases with usernames that belong to a real account, ex: registered e.wasteof.me for @frank, if @e decided to register e.wasteof.me, they would be able to claim the domain back.

and honestly, if someone did have the indecency to take a huge amount of domains just to stop other people from having them, I would just give priority to whoever wants one of them.