Hmm, my first gut response was 'wtf, there are so many development tools for Linux, it's insane.' But you're trying to stick with .Net which was created by MS and yeah it's kind of crap even after all these years on Linux. So really you should be saying 'Development with .Net on Linux is decades behind'. Mono has gotten better, and SDL2 is fantastic. But trying to port .NET code over when there are many parts Microsoft made sure were not cross-platform, it makes it rather difficult to try to take something that was coded initially around only supporting Windows to some other platform.
Well, looking forward to Launchbox being native. Maybe ping some people over on gamingonlinux.com to see if they can help out?