So what do you use real arrays for? For 80% of programming lists are just fine. Are you doing cpu-bound numerical calculations?
All kidding aside, unless I'm interviewing at an Elixir shop, I've learned that Elixir is a little too weird for interviewers who don't know Elixir very well.
This occurred somewhat recently when implementing stable topological sort. I ended up swapping List out for a Vector (Aja is library I used). I received a 100x performance improvement from it.
That's really the only time I've truly hit a List performance roadblock in 7+ years of Elixir.
With a big caveat that modifying tuples isn't great for performance unless the compiler or optimizer determine that mutating the tuple is acceptable rather than providing a mutated copy.
Even clojure's is a cheat.