The iconography of Heracles in ancient times was as famous then as let's say a person holding/being affixed to a cross would be now. Not to be a smart ass, just to provide some sort of modern day simile

It didn't end up in the sewer. Not in an ancient sewer anyway. It just got discovered when a modern day sewer needed repairs. No mention of ancient sewers in the article. Wouldn't make sense either, since where it was found would have been outside of the ancient city of Rome. No sewers there.

This is true. Of human beings. Not of gods. The combination of the naturalistic appearance and the provenance along side the Appian way, famous for it's many funerary monuments led me to my suggestion. That's all

The face looks to be a portrait of an actual person rather than the immortal flawless (demi-)god, so maybe it belongs to a funerary monument with a statue of the deceased depicted as Hercules, not unlike Commodus had himself depicted as this greatest of Greek heroes.