[infinity0]

Well, FWIW worth that's not the primary reason I like those languages. It's the safety.

After some experience with immutable data structures, you know how to make them efficient. For example most of the time you don't need to copy that much data - if you need to change a small part of a large data structure, you arrange it so you can re-use (re-point to) the parts you didn't change. On average you should be able to reduce your cost down to O(log(n)) which usually is "good enough".

That is the correct trade-off IMO - have a newbie start off writing safe code, that gets quicker and less memory intensive with experience. Not start off be blazing quick but unsafe, then add the safety with experience.

Did you know Rust (which defaults to immutable) is currently head-to-head with C in Debian's "fastest languages" comparison?

https://benchmarksgame.alioth.debian.org/u64q/rust.html