> If you don't optimize power consumption you're going to increase surface area required to build it. There are hard physical limits having to do with signal propagation times.

While true, that probably stopped being an important constraint around the time we switched from thermionic valves to transistors as the fundamental unit of computation.

To be deliberately extreme: if we built cubic-kilometre scale compute hardware where each such structure only modelled a single cortical column from a human's brain, and then spread multiple of these out evenly around the full volume within Earth's geosynchronous orbital altitude until we had enough to represent a full human brain, that would still be on par with human synapses.

Synapses just aren't very fast.