I think there are quite fundamental differences to the LLM model equivalent to an adult human mind and current LLMs (even accepting an LLM can model a human brain, which I don't think is a given - but I also don't think it's impossible).

The details matter (training set, full context). I doubt our current LLMs knows what smelling cut grass on a wet morning feels like, or how the stomach flutters on a first kiss - even if they have "read" tens to hundreds of attempts at describing such things.

You're essentially suggesting we play Turing's Guessing Game; if your LLM can guess my response to any prompt - then it can be said to have modeled how I would reply to those prompts. Expand the prompts far enough, and you could reasonably argue the LLM models me.