The Lanauder limits on switching energies is one bound, but most of the energy (in brains or modern computers) goes to wire transmission energy, and one can derive bounds on signal propagation energy in the vicinity of ~1pJ / bit / mm for reliable signaling.

The energy count for signal transmission doesn't include changing the amount of ion channels a neuron has. You might model short term plasticity but you don't get long term plasticity.

You also don't model how hormones and other neurotransmitter float around in the brain. An ANN deals only with the electric signal transmission misses essential parts of how the brain works. That doesn't make it bad for the purposes of being an ANN but it's lacking as a model of the brain.