Exactly. It's a meaningless and even misleading analogy. If forced to draw a comparison, you could maybe talk about the energy dissipation of a single neuron

Exactly. It's a meaningless and even misleading analogy. If forced to draw a comparison, you could maybe talk about the energy dissipation of a single neuron and compare that to, say, the energy dissipation of a single transistor. And in that case, considering a human brain is powered by something on the order of 10^10 neurons, the energy efficiency of the brain comes out looking pretty good.