Have you seen the AWS go sdk? It basically builds linked lists (no locality) of everything and marshals to and from json over and over like it's free. I mean there's no thought whatsoever to making efficient use of memory, getting locality for improved performance, etc.

And if you think about it, most things using the aws sdk are network i/o bound anyway, which is probably why they burn ram and generate garbage like it's free.

So immutable data structures (especially persistent ones) aren't a problem at all in many domains.