Efficiency has everything to do with it. To run your original thought experiment would likely take more computing capacity than humanity will ever produce with current silicon based processors.
It could be that we can "get there" with much rougher approximation, but that is by no means a given. If "getting there" does require a much more complex model that actually involves simulating human neurons with much more accuracy and precision, the computing power and energy needed, again based on semiconductor computers, might simply be intractable.
I'm no more suggesting that you actually attempt to build an ANN to run a full quantum simulation of a person and their house than Einstein was suggesting that you go out and board a train that goes the speed of light. The reason it's called a thought experiment instead of a project proposal is that actually doing the thing isn't the point. It's about examining the consequences of a premise.
The difference between your thoughts experiment and Einstein's is that Einstein's had some testable implications. Yours is closer to belief in a teacup drifting in deep space.
The entire premise is unfalsifiable because it requires construction of an impossible thing:
> If you made one big enough to very closely approximate the entire quantum state of a person interacting with an environment, would you still declare that nothing it could do is "thinking"?
It could be that we can "get there" with much rougher approximation, but that is by no means a given. If "getting there" does require a much more complex model that actually involves simulating human neurons with much more accuracy and precision, the computing power and energy needed, again based on semiconductor computers, might simply be intractable.