took decades and hardware capabilities for mainstream to realize that immutability can be extremely good for 1) people reasoning 2) machine execution.

Immutability is quite the opposite of good for machine execution. Much of modern CPU architecture is based on the idea of memory locality, and that you'd be reusing the same memory addresses in a given unit of work.

Also, immutability helps people reason when the language doesn't have a clock. If the language does have a clock -- i.e. it is synchronous, like Eve or Céu -- mutability poses no difficulty.