It begs he question - how much of the size of the brain is related to functionality and how much just to ability to store information. Is greater brain size due to greater (more complex) functionality or just more, and more complex information handling. One wonders.
I have long suspected that a huge portion of brain activity is ‘operating system’
While you may have one or a few conscious thoughts going on for a given task or tasks, they can instantly be preempted by a touch on your arm or a loud sound or something else that demands immediate attention.