I've just recently ported a python/Django site to c#/.NET. The switch was not done for performance reasons (or community for that matter) but as a consideration the .NET version was an order of magnitude faster on the same hardware without any effort to optimize.
All of this is accurate, and he's wise for leaving .NET
It's just not the environment or kind of people you'd prefer to work with, given better communities and concentrations of driven programmers you could be working with.