What you say would make sense in a hypothetical world where every JITter could work with every language, but that's not the world we live in. You can just hand chef B better-quality ingredients and have him do his thing, but you can't just hand HotSpot MSIL code and have it do its thing. Half of this is due to differences in the representations. The other half is because MSIL has features that (as far as I know; please correct me if I'm wrong) the JVM doesn't have, such as by-ref variables, which it would still need to support, but which might make optimizations such as escape analysis harder.

This is why people judge chefs independently from the ingredients they are given, but don't judge languages and implementations independently from each other. In the first case they are actually (mostly) independent in the real world, whereas in the second case they are frequently dependent on each other, and it is not possible to mix-and-match languages with compilers. (But I certainly do hope we get to a point where the latter would be possible, too.)