Yours is exactly the right intuition imo.

If you presuppose certain key aspects of materialism, non-dualism, functionalism, objectivism, perhaps absolute determinism... and then layer on a good general grasp of neurobiology, chemistry, cosmology, physics, computer science, evolutionary biology, and psychology... I think the conclusions you have stated are inevitable.

Humans are "just" atoms. Humans are "just" the sum of trillions of living cells going about automatic/reactionary processes, culminating in a buzzing cacophony of activity that gives rise to what we perceive as consciousness and free will.