Everything you say is true, and more. There is another kind of cell in the brain that outnumbers neurons about ten to one. They’re called glial cells and they come in numerous forms. We used to think they were just support cells but more recently started to find ways they are involved in computation. Here is one link:
https://en.m.wikipedia.org/wiki/Tripartite_synapse
The computational role they have is unclear so far (unless there is more recent stuff I am not aware of) but they are involved.
We are nowhere near the human brain. I think it will take at least a few more orders of magnitude plus much additional understanding.
GPT-3 only looks amazing to us because we are easily fooled by bullshit. It impresses us for the same reason millions now follow a cult called Qanon based on a series of vague shitposts. This stuff glitters to our brains like shiny objects for raccoons.
What this stuff does show is that generating coherent and syntactically correct but meaningless language is much easier than our intuition would suggest:
https://nbviewer.jupyter.org/gist/yoavg/d76121dfde2618422139
Those are extremely simple models and they already produce passable text. You could probably train it on a corpus of new age babble and create a cult with it. GPT-3 is just enormous compared to those models, so it’s not surprising to me that it bullshits very convincingly.
Edit: forgot to mention the emerging subject of quantum biology. It’s looking increasingly plausible that quantum computation of some kind (probably very different from what we are building) happens in living systems. It would not shock me if it played a role in intelligence. The speed with which the brain can generalize suggests something capable of searching huge n-dimensional spaces with crazy efficiency. Keep in mind that the brain only consumes around 40-80 watts of power while doing this.