Humans have a huge amount of "common sense" knowledge that makes object recognition a lot easier, even without 3D information.

Even with only one eye, it has to focus differently for different distances. I think that information is somewhere present in the brain and can be used (even when not consciously accessible)

Some VR users (and IMAX 3D customers) have reported 'learning' stereovision.

I'm pretty sure I'm stereoblind. I think my brain is too lazy to combine images into 3D. Pot seemed to kick my brain into overdrive and process that signal. My friend laughs at me for "seeing in 3D for the first time" and doesn't believe me.

The brain is also hardware, just extremely efficient. When compared to modern processors, the visual cortex does way more while using less energy.

The human eye has some interesting optical defects like chromatic aberration that man-made optical systems usually fix in hardware but that the brain fixes in software. These aberrations, when available to the software as uncorrected input, can provide information useful for determining how to focus properly (and by extension, focus distance, which gives you distance-to-point information dependent on DOF). [1]

Modern photographic lenses tend to contain a large number of lenses in series, a few of which often have an exotic property like being apochromatic, aspheric, or made of fluorite, but such well-corrected lenses may be counter-productive for machine vision. Phase detection in a DSLR relies on separate collection sites like stereo vision, but autofocus still hunts under bad conditions.

[1] https://www.ncbi.nlm.nih.gov/pmc/articles/PMC3189032/