It was made for GDScript as much as GDScript was made for it.
Both the C# and Rust integrations work, but they feel so wrong because the whole engine was designed in this ultra-dynamic style. You end up writing different code than you would otherwise when using those languages, to an even greater degree than in other engines. You end up writing GDScript with a different syntax.
I'm not saying the GDScript way is fundamentally wrong, and besides this issue I think Godot is a great engine, but it is clear that in the current scheme, every other language is a second-class citizen.