Rust is very good at making things immutable. But that doesn't mean it's particularly fun to, for example, append or prepend something to a list and retain a reference to both the old and the new list.

Compare to most "functional" languages, in which prepending an item to a list and ending up with immutable references to the old and new lists is almost the defining feature of the language.

Considering the performance implications of a full commitment to immutable data structures, I think Rust does a pretty good job here.

Dynamic arrays / vectors / slices or whatever you want to call them are probably the most important or fundamental non-plain-old-data data structure, and in a purely immutable environment these are essentially impossible (or have awful performance characteristics).

Yeah although I find FP languages' obsession with singly linked lists to be a real flaw because they have such awful performance characteristics. And also pretty bad ergonomics often. The number of times stuff comes out backwards...