Agreed, GDScript is pretty nice for working with the engine.

> The problem isn't just Ruby speed, it's that GDScript exists and Ruby doesn't really offer any benefit over it. If there were no scripting language, sure, hook up Ruby.

However, I'm inclined to say that familiarity with a language might be reason enough to choose to use it, if there are no other significant dealbreakers! If you like C++, use C++. If you like Rust, use Rust. If you like Python, Lua, or Ruby use those... as long as someone has done the work to make that possible (or you want and can do that yourself).

GDScript is nice and easy to pick up, but someone who has used .NET for close to a decade might benefit from using some C#, or maybe they like the refactoring or other functionality that an IDE like JetBrains Rider might provide, especially with the occasional nice plugin for the engine itself popping up: https://plugins.jetbrains.com/plugin/13882-godot-support (to be honest, I really liked the Rider plugin for Unity as well, which made writing code a more pleasant experience).

Secondly, there's also the question of an ecosystem, which may or may not work depending on how well any runtime integrates with the engine and what the situation for packaging various libraries/dependencies is (since sometimes you need to deal with native code in Ruby and others). But when it works, you can get a library for basically anything you might want to do: a novel game with AI processing? There are libraries for that. Want to hook up your own netcode solution? There's probably a solution for that. Want to do compression, or work with a variety of file formats, or add dynamic scripting, or interact with a web service of some description? Those are solved problems in some languages, with the solution being just a library away.

Of course, most games probably don't need anything that fancy and the engine has bits of nifty functionality in it, like making web requests, for example, but overall being able to benefit from a rich ecosystem is also good, especially when you decide to do something a bit more novel.

At the end of the day, use whatever works for you: for someone that might be GDScript with its nice integration with the engine and easy syntax, for someone else that might be C# with its static type system and rich IDE support, whereas someone else might be a bit more brave and go off the beaten path further!