Maybe it helps if I explain better. I find it difficult to use immutable structures if I want certain performance characteristics. It's possible I need more training in certain techniques, but I think that's why I find it difficult, the default data structures and introductory literature seems to be too naive. And in the end, no matter what I use, there will be certain trade offs for purely immutable structures, and some stuff I just think it's easier to think about in mutable terms.

OK, that's a reasonable position. It is easy to read your original claim as "All real world programming requires mutable values", and that is certainly not a reasonable position.