They have been improving, this is one area however where those C# vs Java flamewars kind of miss out.

While C# the language has much more goodies than Java the language, Java the platform has had much better options than the CLR, because it has been mostly Microsoft and Mono (nowadays almost gone after the acquisition), whereas the Java ecosystem has a plethora of implementations, each one wiht their JIT and GC implementations, even AOT caches since almost three decades now.

Thankfully the outcome of Project Midori, and the whole Secure Future Initiative , has had the side effect of Microsoft becoming more serious about .NET performance, instead of always outsourcing performance workloads to C++ and COM.