I agree about the lack of documentation for C# but C# language support is still young not complete.
I think one of the things that make Unity so great is how easy it is to find solutions to a new problem. In many cases you can just google what you want to achieve and most likely you get a hit on the community forum where someone has already published code for you to basically copy and past.
We do not have a big C# community in Godot yet. The majority like GDScript. I personally like compiled languages as I find them easier to work with. One way we can grow the C# community is to start using the community forum more. Ask more questions and help others so it is easier for new and existing users the find answers, tips and tricks. Remember to tag stuff with C# and or Mono so we can more easily find the questions.