I feel that was more true 1-2 years ago. These days I find Claude Code write almost as good (or as bad depending on your perspective) Elixir code as JavaScript code and there must be less Elixir code in the training data.
I personally find it much more painful to generate valid Rust code that compiles and does what I want than e.g. valid python code that runs and does what I want.
in my daily experience Claude Code writes better Elixir code than JS (React). Surely this has to do with the quality of the training material
There's certainly a lot more JS code out there to train on, but the quality of the Elixir code is likely overall much better.