GDScript is not very maintainable as the code base grows. It lacks proper refactoring tools (e.g. the ones from Jetbrains Rider), static type checking, flexible object system and many 3rd party libraries which might be needed

My main point is: if GDScript isn't good enough, go straight to c++ directly in the Engine.

I won't even get into how big of projects I've written in GDScript successfully.