> What’s not great is loading the entire closure VM environment into my browser

There's no VM in clojurescript, it compiles to JS, it is tree-shaken and heavily optimized and minified through Google's Closure compiler.

> resulting in the software running (in this case) 50x slower

The speedup is not a result of abandoning clojurescript, it's from moving from immutable data structures to mutable arrays and primitives. The same can be done in clojurescript or javascript.

I think this is a common misunderstanding, that's why I'm reacting. Nobody claims immutable data structures to be the silver bullet. Computation-heavy parts need to be done in low level code and with primitive types.