Would you call TechEmpower benchmarks synthetic? I think they're a pretty useful data source and indeed support the claim that the performance of .NET is rather good.
https://www.techempower.com/benchmarks/#section=data-r21
Personally I think that some of their tests are pretty close to what web applications might actually do a lot of the time (fetching the data, processing it, saving it), for example, see here: https://github.com/TechEmpower/FrameworkBenchmarks/tree/mast...
Sure, sometimes the code you see in benchmarks can be a bit more clever than the code you'd see normally, but for the most part TechEmpower seems close enough to be a vague indicator towards what frameworks/languages/stacks have decent performance.
It also helps you get a feel for how big the differences are between any two given platforms, like using something like Java + Spring and Python + Django, which may or may not be relevant in actual business conditions, since you might also want to iterate quickly.