As an professional .NET Programmer, i want to say few things.
Java to C#
I read many of your comments that are talking about simple porting from Java to C#, so it still suck!. I could say that i agree with you. However, byself, C# offers many benefits that make it better even if it is simple copy/paste to other language.
C#, byself is about 34% faster than Java and in MANY cases can be 200%+.
You can achieve much better/faster/stable lineage 2 server with changing some parts. Like Database communication, Networking etc. These processes can be much much faster in C# and it is not big work.
As about DDOS,
Don't joke yourself. Even C++/ASM Server will crush after a high DDOS Attack. Nowdays nobody use "exploits" of your code to take down your server.
Before few years where java had many security issues, we could say that C# can beat exploiters... Now, 2016, both languages offers you security (even with bad code).