Well it has always been performant. The whole Stackexchange is built with ASP.net, and it render things 10x faster than Ruby Rails while requiring 10x less hardware resources.
[1]https://nickcraver.com/blog/2016/02/17/stack-overflow-the-ar...
[1]https://nickcraver.com/blog/2016/02/17/stack-overflow-the-ar...
"The degree of improvement is absolutely astonishing, going from 2,120 requests per second on Mono in Round 11 to 1,822,366 requests per second on ASP.NET Core in Round 13. That’s an approximately 85,900% improvement, and that doesn’t even account for Round 11’s hardware being faster than our new hardware.
That is not a typo, it's 859 times faster! We believe this to be the most significant performance improvement that this project has ever seen."
That's why the increase was so significant. If they were comparing ASP.NET Core with .Net Framework on Windows, the difference would have almost certainly been much smaller.