To be fair most of the brain is more like a pretrained model — it isn't being trained at any point after conception to keep your blood pumping or your lungs working, it does that out of the box roughly as soon as you sprout those organs (or the minute you're born, in the case of lungs). The training process was billions of years of evolution. And, well, given fairly persistent cross-cultural cognitive biases, I expect the conscious thought parts are starting from a pretrained model, too, and all we're doing in school is finetuning ;)

People don't understand that to simulate a single neuron, you need an entire neural network. So 70 billion parameters might at best be equivalent to a million neurons but that is assuming that your neural network architecture is akin to the connections between neurons. Considering the physical sparsity, you might need even more parameters to model the connections of a biological neural network. So less than a million neurons in practice.