I think many were more concerned about .NET performance against tech in the same class, mainly the JVM, which previously blew .NET out of the water in the benchmarks for a number of years.

From the Techempower blog post I linked to above:

"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."

In the past, TechEmpower benchmarks only ran on Linux, so their benchmarks for .Net actually used the Mono project's implementation of ASP.NET, which was slow.

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.

I saw claims of a 30% perf increase moving to .net core for a major software company. Can't remember which one, but that's still pretty impressive...

Perhaps you're thinking of Microsoft moving Bing to ASP.NET Core 2.1, with a 34% performance improvement: https://blogs.msdn.microsoft.com/dotnet/2018/08/20/bing-com-...

I see - good point.

Mono has always had terrible performance. It was mostly useful as a way to sell developers who wouldn't normally go for a Windows-only solution on something that was effectively Windows-only in practice, if you cared about things like performance.