The complexity and scale with LLMs come from the amount of training data used, not some kind of black magic in the programming.
Not really. We cannot model physics and chemistry to a level which allows us to accurately predict a humans action (even a tiny time-step into the future)
This is vastly different to an LLM, where the model is the model (for a lack of better phrasing).
You could just as easily say that if you can write a python interpreter that you can understand every program written in python. Ok, now what if the program is two terabytes?
A frontier LLM is nothing but a 2 terabyte program written in a weird programming language. Just because you can understand the interpreter does not mean you understand the program in a meaningful way.