Brains are not simple so many “just common sense” theories have fallen by the wayside. Michael Denton takes up the question in The Miracle of Man (2022):

Neuroscience researcher Michel Hofman, who describes the human brain as “one of the most complex and efficient structures in the animated universe,” Denton, noting that a cubic millimetre of human brain features sixty times as many synaptic connections as a 747 jetliner has components, goes on to say: “Many authors have concluded that it may be very nearly the most intelligent/ advanced biological brain possible. That is, its information-processing capacity may be close to the maximum of any brain built on biological principles, made of neurons, axons, synapses, dendrites, etc., and nourished by glial cells and provided with oxygen via circulation. For example, Peter Cochrane and his colleagues, in a widely cited paper, conclude “that the brain of Homo sapiens is within 10– 20% of its absolute maximum before we suffer anatomical and/ or mental deficiencies and disabilities. We can also conclude that the gains from any future drug enhancements and/ or genetic modification will be minimal.” Hofman concurs: “We are beginning to understand the geometric, biophysical, and energy constraints that have governed the evolution of these neuronal networks. In this review, some of the design principles and operational modes will be explored that underlie the information processing capacity of the cerebral cortex in primates, and it will be argued that with the evolution of the human brain we have nearly reached the limits of biological intelligence.” (p. 193)” If Hofman, Cochrane and colleagues, and Denton are right, recent proposals to increase human intelligence “within a decade” via genetic engineering are doomed.
News, “Why some life forms are smarter than others is still a mystery” at Mind Matters News (July 14, 2022)
Takehome: Genetic engineering probably wouldn’t make humans smarter because, as biochemist Michael Denton notes in Miracle of Man, our brains seem to be optimally organized now. That would seem to support a design hypothesis.
You may also wish to read: Ever wish you had total recall? Ask people who do… Recall of every detail of one’s past works out better for some people than for others. Just why some people can recall almost everything that happened to them is a mystery in neuroscience, in part because they are few in number.
As to: “(the brain’s) information-processing capacity may be close to the maximum of any brain built on biological principles, made of neurons, axons, synapses, dendrites, etc., and nourished by glial cells and provided with oxygen via circulation.,,,”
Shoot, in terms of ‘information-processing capacity’, the brain also greatly exceeds any supercomputer that man has ever built,
From the preceding findings, one would ‘naturally’ presuppose that if you had a bigger brain then you would be more intelligent.
But that is not what we find. Intelligence does not have a direct correlation to brain size.
In fact besides intelligence not directly correlating to brain size, and in a finding that should give Darwinian materialists sleepless nights, “Despite removal of one hemisphere, the intellect of all but one of the children seems either unchanged or improved.,,, Intellect was only affected in the one child who had remained in a coma, vigil-like state, attributable to peri-operative complications.”
In fact, “Another study found that children that underwent hemispherectomies often improved academically once their seizures stopped. “One was champion bowler of her class, one was chess champion of his state, and others are in college doing very nicely,”
Here are a few more examples that defy materialistic expectations,
Obviously, having high mental capacities, despite missing half, or more, of your brain, is simply inexplicable for those who are wedded to the belief that the mind is reducible to the material brain.
Yet this ‘anomaly’ is a persistent pattern that is found in neuroscience. As Dr. Michael Egnor notes, “what we find, (in neuroscience), doesn’t fit the prevailing view that the brain runs the mind as computer hardware runs software.,,, We can do better science—and medicine—when we recognize that human beings have abilities that transcend reductionist material explanations.”
And as if the intellect remaining unchanged, or improved, despite the removal of half the brain was not bad enough for materialistic presuppositions, in Near Death Experiences it is reported that people routinely have “enhanced thought processes [that] takes place when the brain is not functioning well or sometimes not functioning at all,,”
Again, such findings are simply inexplicable for those who are wedded to the belief that the material brain generates the mind.
Verse: