sadly, disembodied brains are not very useful. embodied brains require a civilization's worth of energy consumption and environmental impact in order to do their work. so we really need to take the world's power/water/carbon impact (divided by the world population) to talk about how much power it takes for a human brain to solve a problem.

An LLM takes twenty seconds to write a page. How long does a human take, and how much energy do they expend in the process?

For some given task, perhaps; but the AI only consumes power while actively working. The human has to run 24/7 and also expends energy on useless organs like kidneys, gonads, hopes, and dreams.