I think you’re sidestepping the point here. The point is that the combo of these systems becomes one unit. One integrated system. That’s the new system to measure. Similarly, your prefrontal cortex without a hippocampus sucks. The combo of them (and other distinct parts of the brain that handle specific functions and have specific purposes that interact with other parts in a specific way) - that is what causes our specific type of intelligence to emerge. The brain as a whole is much more interesting and practical to measure.