I think the “some years ago” is pretty relevant.

.NET has heavily invested in performance. If I understand your article correctly, you tested .NET 5 which will be much slower at this point than .NET 10 is.

I also think it matters what you mean by “Mono”. Mono, the original stand-alone project has not seen meaningful updates in many years. Mono is also one of the two runtimes in the currently shipping .NET though and I suspect this runtime has received a lot of love that may not have flowed back to the original Mono project.