I think a lot of the pain in Scala/Rust etc immutable data structures comes down to static typing. In Clojure for instance you can very ergonomically do deeply nested persistent updates.

    (update-in
     {:foo [{:bar ["a"] :baz ["b" "c" "d"]}]}
     [:foo 0 :baz 1]
     clojure.string/capitalize)

    => {:foo [{:bar ["a"], :baz ["b" "C" "d"]}]}