I agree with everything what Dizaka wrote, very well summarized, and as Dizaka described we spent significant time on some effort to track the username which was harvesting IPs at that time, Dizaka described the process how we did it and unlike him I believe we were able to narrow the username down. The question now is - How does that help?
First of all, nobody would believe me that we did it honestly and correctly and with no offence most of the people do not even have technical knowledge to understand it to make correct judgement. Anyone could just say that we picked someone we didn't like.
And second of all, the username was using VPNs to connect to the lobby, their IP kept changing and I bet they use multiple accounts. Block one username or IP address and the ddoser will just create a new account from different IP provided by a VPN.
We can make it more challenging for the ddoser as Dizaka described but there is imo no ultimate solution with the way how the game hosting works/size of the community/no will of players to do anything to prevent the ddos and obviously anyone who's been doing that for more than a year has enough motivation to get through some barriers.