I am puzzled, what are these statements based on? "Linux stacks were either PHP, Rails, Django, or similar, which, while good, are not as performant." - first time I hear a .NET/Windows/SQL Server stack is more performant than these.
SQL Server has huge amounts of tuning and cooperation with NTFS driver team to ensure good performance, and frankly, it's at the high-end of the databases, and I really wouldn't mind using it except for price :(
Not sure how the story goes for Rails, but Python (Django) used to be a pig when SO was started over a decade ago, for similar reasons as PHP.
Django's execution model is not at all similar to how PHP code is being run. Pretty much every python web server uses wsgi (or mod_python before that) which relies on a persistent app server. Whatever are the reasons for django's assumed performance issues, PHP's runtime model had nothing to do with it.
C#.NET performance is up there with C++. C#.NET is only slower than C++ during garbage collection. When garbage collection is done, it is back in business and running at the same speed.
That's not a great summary. .Net is complex. There's AOT compilation but not available for all purposes. There's JIT which applies most of the time to C# code compiled into msil. From there different things can happen depending on implementation, which may also include running the code via an IL interpreter.
Put those things together, and it’s fairly evident that C#/.Net greatly outperformed the Django/Rails stacks that were popular at the time.