And language itself is so very 'stochastic' too, due to complex subjectivity. Every word floats on a variable sea of individual choice.

For example, if I compose your post as :

--

"Good prose embodies intellect gradually evolved by myriad humans over time, so it wows me to see LLMs create it, though I soon realised that the intelligence is not being created by the LLM but rather is already present in the human-evolved input datasets - the prose itself! - which they statistically arrange."

--

..the particulars of the language are entirely different (and omit some of your chosen nuance) but most readers would receive the same "core truth" from it, the same measure of beneficial information.

Which highlights the great fluidity of language; that is another of the key underlying mechanisms allowing LLMs to flourish.

I think there is a distinction to draw there between stochasticity in the use and in the evolution of language (which is not clean as they are not independent). The language evolves stochastically, as it does so by being used in exchanges. But the use could be deterministic with the exchanges being random and the function of update based on exchange. I still think there is stochasticity in the use itself, I choose my words, go back and delete and rewrite, explain again in a different way when the audience looks at me unimpressed etc. I just don’t see fluidity as a proof of stochasticity of evolution or the other way around and in fact think the interaction is a quite interesting domain.

I present this as by-no-means a complete argument, but a very salient point imo is the notion of the 'accent'. It is the most prominent etymology mutation in language (driving inter-language variance between adjacent cultures), and exists not only in the human but in the animal kingdom. Its basis? The maxillofacial expression of the most dominant speaker(s) within a group, which shapes their vocal inflection and passes to the wider culture by social effect.

Regardless, the fluidity of language is self-evident to an extent : it is partly embodied in the entire concept we call figures-of-speech (a linguistic phrasing can be literal, or sarcastic, or described by metaphor, ...). Partly in the common reality that our dictionaries list multiple possible definitions for many words. Partly in the fact that (many) synonyms exist. Partly in sheer human individuality.