I prefer having the numbers as opposed to globally unique usernames. It destroys the incentive to steal high value usernames through scams and social engineering attacks. I don't get random friend request from people who aren't even in servers I am because they don't know the numbers to send a request. It also gave Discord a reason to sell Nitro because for a fee you could just change the numbers to 1234 or whatever. You will see an increase in scams as people aim to steal high value usernames to resell them as well as an increase in spam. We've seen this behavior on Twitter for years.