If you look at an integrated circuit like a CPU at the gate level, you will find complexity which goes beyond the logic being implemented -- the snaking physica

If you look at an integrated circuit like a CPU at the gate level, you will find complexity which goes beyond the logic being implemented -- the snaking physical routing of the traces; the width and layer of the traces; supply and ground lines; the orientation of the gates; the number of fins on a multi-gate finFET. Someone without a high-level understanding may wrongly assume that any of these things contribute to the logic. Sometimes specific details are important, yet do not encode higher-level information. Supply lines must be able to carry enough current, so changing their size may break the logic. Clock distribution lines must propagate their signals at the correct rate, so changing their length may break the logic. Neither of these factors need be considered in a high-level emulation of a processor. In the same way, complexity in the brain may be irrelevant to its function, redundant, or even problematic. As an example: the vascular anatomy of the brain is complex, but not generally considered to be instrumental to cognition; it's similar to the Vdd and ground, but shapes the neural matter around it. As we don't understand the mechanics of how intelligence arises from neurons, it would be wrong to assume all their properties are instrumental. Given that an integrated circuit is an engineered system, and the brain is a evolved biological system, and evolution is in many ways more prone to unnecessary complexity because of local optima traps, I would speculate that much of the brain's complexity is likely not instrumental to intelligence (yet may be contributory).