[Matthias247]

The point of the parent was that better performance is not guaranteed, and it's totally true.

E.g. go ahead and implement a RPC server which e.g. only has to deal with 10 concurrent requests - then measure latencies. The synchronous version might be faster, due to not requiring any epoll calls. The different might get even bigger if e.g. the server is serving static files, and you are measuring throughput - the synchronous version will likely provide higher performance since no extra context-switch from the async-runtime-of-your-choice to threadpool-for-file-io thread and back is required.

You are also right in that once one moves beyond a certain scale the async version might offer better performance. But the scale that is required would be different per application, and not every application requires the scale.