"We know that’s how the human brain works, at least directionally."
That's an extreme misrepresentation. What happens inside a human neuron is still not properly understood, it's not as simple as a probability function. And the network itself is certainly not feed-forward. Of course LLMs draw inspiration from the brain, so there are some similarities. But because of the language-trick of using terms from medicine and cognitive science to describe LLM architecture, we see a lot of faulty reasoning from the so-called "rationalist movement".