There's also Dialyzer (and various IDE integrations) for some level of static type-checking.
elixir people really should learn erlang.
if you ever saw a coffeescript person struggling to do things that are straightforward in js, because they didn't bother to learn js? that's what you're doing now
If you learn the base language, you get more powerful in the descendant language as well
Only you DO use languages that end up as machine code, and the idea of understanding machine code to better utilize something like C isn't outlandish.
No need for extra build tools, FFI with the platform language, additional debugging tools, the urge to create wrapper libraries that feel more idiomatic into the guest language, waiting for the guest language to come up with ways to expose new platform capabilities,...
Guest languages are good for experimenting new ideas that eventually get adopted by the platform and then the world moves on, and they turn into the next CoffeeScript.