I try to change all accounts to an actual username when possible. Test sites/offline sites get admin as the name XD
Luckily I don't use wordpress, so this isn't going to bother me lol
That's what I did, it seems to work fine. I can log in no problem with the new username etc. Posts are still assigned OK to the admin user with the right nickname.
No idea why WP doesn't let you do this from the admin side. I must admit it did seem a little too good to be true, just changing one entry in the database.
We've been dealing with those attacks all last week and this week at work. Thankfully no accounts with the username admin, but we've been blocking IPs as fast as we can detect them.