.NET core impl has 2 versions, async and sync. Task.FromResult is synchronous, yes. Look closer :)
I am having hard time understanding what you are trying to test here. I am worried that .NET code is not really testing what you think it is.
[1] https://msdn.microsoft.com/en-us/library/dd997402(v=vs.110)....
Maybe you mean we should schedule something which has a complete event loop? That would be a lot more fair wrt the Akka version, but the Go version does not create any threads either.