Also how useful is quantum chemistry.

You can probably just "memorize the rules" with a neural network, the way protein folding was solved, and not actually simulate the quantum chemistry. This is drastically faster and almost as accurate.

This means you just do a bunch of chemistry experiments, or load in the data from already performed experiments, and figure out the rules so you can predict the experiments you didn't perform. Neural networks can already learn most possible functions so they can approximate what a quantum chemistry sim would theoretically be exact for.

And the approximations can be potentially just as accurate : remember your input data has finite resolution. (significant figures)