> I wouldn’t spend too much time learning programming languages outside that list as you need more tools in your toolbox but too many tools may get your toolbox cluttered
You suggest not cluttering your toolbox, but your recommendation is a list of completely interchangeable dynamic languages?
I would recommend learning either language outside the context of a framework like Rails or Phoenix, though. There's immense value in knowing the underlying libraries (Rack and Plug, respectively) and the HTTP servers underlying those (Cowboy and Unicorn/Puma/whatever-is-popular-nowadays, inverse-respectively). Once you know those, you'll either gain an appreciation for the existing frameworks or have the know-how to improve and/or replace them.
Elixir is compiled, the other two are interpreted.
JS is supported natively by all browsers and is at its core an event-driven functional language, the other two are not.
Ruby is probably the comfiest OOP language out there, and certainly the one with the best standard library.
These are not the same languages.
What does Ruby's standard library have that makes it superior to Python's?
How can a language be intrinsically compiled or interpreted?
Sure, Befunge is one example of a language that's notoriously hard to build a compiler for but easy to build an interpreter for, but surely that can't be said for Ruby and JavaScript. V8 is a good counter-example to the claim that JavaScript has to be interpreted.
This is a great example of an academic nondistinction that is completely worthless in practical matters.
It's precisely in academia where it is a worthless nondistinction, there a language doesn't even need to be implemented to be studied. For instance lambda calculus predates the programmable computer.