It's not a massive leap of faith at all. Two reasons:

   1. We know how natural selection works, and it clearly often produces unnecessary parts for many things.
   2. There is physical evidence of evolution creating unnecessary and inefficient parts and components. 

1. Natural selection works by randomly creating a fixed set of features both bad and good and then selecting the best one. Thus the features are bounded by randomness. If the random mutation doesn't create the most efficient part then The only thing that can be selected is an inefficient part. This follows that it is VERY possible that many processing modalities of the brain CAN be unnecessary. It is NOT a massive leap of faith.

Additionally the selection criteria is simply survival. Not efficiency. As long as the "processing modalities" in the brain aid in survival the selection process does not interfere. Thus all kinds of arbitrary processing modalities both efficient and inefficient can occur so long as the modalities do not detriment survival. Why does stupidity evolve? Well stupid people aren't smart enough to create nuclear bombs to kill themselves. Thus stupidity is a possible trait, similar to how inefficient and unnecessary "processing modalities" are possible, mayhap being stupider aided in survival or didn't contribute anything at all. Just looking at people responding to me on HN, alot of them are pretty stupid (physical evidence). Not pointing out which one, certainly not you.

2. There is (alot) of physical evidence of the above. For example, the wheel is a very efficient way of traveling yet no animal has evolved some form of a wheel. The reasoning is actually more complicated about why a wheel hasn't evolved but the general idea I described above still applies... both natural selection and random mutation were not able to generate the series of intermediate traits required to form wheels.

Thus from the reasoning above it is very possible for the brain to evolve with unnecessary and inefficient "processing modalities".

Yes this idea did begin as a gut feeling. Subconscious processing is often times correct and logical. It is unwise to constantly mistrust it. It is always wise to analyze these "feelings" in attempt to break down the logic behind why it occurred.

What my self analysis tells me is this: Given the fact that MANY of our mathematical models for physical processes involve elegant and straightforward primitives it follows that intelligence will also VERY likely be such a model as well and very likely much more simplified then the human brain.