Nature has evolved a molecular switch, why the neuron as a cellular switch theory is false

You can easily see just from the size of neurons, that nature would have selected for a molecular switch rather than a cellular one, neurons are 1000x larger than transistors you use to read this.

I believed in neuron-transistor analogy for two years, because of lobbyism from Singularity University actually, but of course neurons are not the "bit" in the brain, they are humongous. Tubulin is.