Yes, I was quite annoyed that Discord decided to abandon their 4-digit numbers. The first place I saw the approach was Battle.net, and was happy to see it when I joined Discord. I'm glad Discord decided to provide the ability to have a separate nickname from your actual handle, but there was no good reason to dump the numbers.

edit: I agree the randomness is important. Without random numbers, the first person to get in will pick "0069".