The only time I've hit this is when implementing algorithms that assume constant time access and modification (a lot of algorithms assume this, and can't be swapped for index based maps easily)

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.