Sorry I don't mean to sound like an evangelist, I just meant that there are misconceptions out there about immutable data structures (functional programming aside: the two are not so intimately involved that they're equivalent).

I hope you can understand why benchmarking OCaml against Java isn't necessarily fair, since they have two completely different implementations (the latter being possibly the most mature set of JIT compilers and runtimes ever built). A more interesting comparison are immutable DAs in languages like C++, for example the immer library which has some very impressive performance characteristics for the problems it solves. And other applications like immutable ropes used in text editors which have extremely high performance compared to mutable variations. At the same time it's not a silver bullet, plenty of other immutable DAs have issues that are non-negligible and applications domains where in-place mutable DSs are required like hard-realtime.

Software engineering is about tradeoffs and not dogma, and that's what I was getting at. A take like "immutable is slow" is the counter dogma to "immutable is perfect."