Now seriously: while reading this, and especially the first problem, my head was shouting "immutable data structures! immutable data structures!".
The author surely must have encountered IDSs during their 10-year tenure with Lisp. I'm curious about why they thought they would not fit the bill for the problems they are writing about.
Secondly, I did read the article. If they are allocating a big chunk of memory and copying it over every single time they are making a change, they are not using immutable data structures. Ok, technically speaking, they might be. But they are using the worst implementation possible as a base to make conclusions from. That'd be like looking at the C language and concluding that strong types are not good, because of all the limitations C has.