That seems like more of a feature than a bug to me. Using C# in Godot means you have all of the Nuget libraries at your disposal, whereas no one is writing libraries in GDScript, because no one is using it outside of Godot.
Meanwhile to extend Godot usefully you have to use C++ and a plugin API that's arguably no less complicated than adapting an existing language as the scripting language would have been.
But that is the thing, you don't have access to all the NuGet libraries, or even CLR/MSIL abilities, it is a hit and miss depending on what platforms are being targeted.
Sure if you only want to target desktop/laptop computers, you're safe.
Meanwhile to extend Godot usefully you have to use C++ and a plugin API that's arguably no less complicated than adapting an existing language as the scripting language would have been.