Please don't make these sorts of comparisons between biological neurons and our "neural networks". They're really not the same thing at all. We'd rather call them "differentiable networks", and IIRC, the human brain is supposed to have only 6 layers in the visual cortex.
Cortical layers are in no way equivalent to DNN layers.
The fair comparison is comparing the number of "free variables" in the system. This is how machine learning models are compared. You don't compare "number of free parameters in linear regression" with "number of layers of neural nets," you compare number of parameters with number of parameters.