I subscribe to this as well, but I still think Doyle has a point. Sherlock wasn't talking about neural biology, but about the structure of the conscious mind. In practice, the advantage of an "efficient brain" might not be very important compared to having focus in one' thinking.

In other words, the problem is not that we have too many pathways in the brain, rather that we spend too many cycles traveling down redundant ones. Let this allegory warn us to accept the scarcity of attention.