Imagine handing a late 1800s scholar a modern processor. Give him a wiring diagram, and a voltmeter. What could he learn from it?
The connectome will be a big step, but not the penultimate one, in solving human intelligence.
However GNNs don’t really capture the underlying mechanisms very well. Our brains use different kinds of Neurons which also use many different neural transmitters, their location in 3D space matters, as do stuff like blood alcohol content, O2 levels, adrenaline, signal propagation delays, etc it’s a stupidly complicated system even above and beyond the number of neurons.