If anything, there is little reason to use a named delegate over the Func nowadays too. The contract in this case is implied by you explicitly calling a constructor or a factory method so a type confusion, that Go has, cannot happen.
The idea with the named delegate would be if you need some way to:
delegate Task<string> GetUserEmail(int userId);
This provides more guidance than taking in a:
Func<int, Task<string>> getUserEmail
If you can annotate implementations of the delegate the tooling support becomes even nicer. Not all Funcs with the same shape have the same semantics, in my ideal C#-like language.
Edit: I completely forgot the main reason which is if using a DI container it can inject the named delegate for you correctly in the constructor. Versus only being able to register a single func shape per container.
