Once upon a time the same was told about Basic, C and Pascal, all serious game development was Assembly.
Then the same was told about C++, all serious game development was in C.
Then the same was told about Java, and a couple of folks not paying attention got millionaires.
Then ...
So many devs get caught up on which language is used. I have my pet languages that I prefer too, but at the end of the day a game engine is about creating games. So long as the language offered is reasonably usable and one can deliver a fun and engaging experience with it, the language bindings don't matter much. Everything I've read about GDScript indicates that it fills the need, is fun to use, and generally gets out of the way so devs can focus on creating fun and engaging experiences.
The only reason I see having C# support is critical is if a Dev is porting from another engine (i.e Unity) midway through development or if the dev/studio has lots of boilerplate code or libraries already written for prior titles. If starting from scratch, I don't see a good reason to stick with it.