Seeds lodged inside the footprints? That's wild.

The "same old coarse steel at the end of each shift" is doing a lot of work in this story, and I'd bet the real fix was the switch from coarse to fine, not from steel to diamond. A worn out or overly coarse steel tears metal off the edge instead of lining it back up, so of course a finer abrasive feels like magic after that. Put a fine cut steel in your hand and you might get most of the same result for a third of the price. Diamond rods are great, but they cut fast and if you keep leaning on them every shift you'll be grinding away good steel and shortening the life of that boning knife. And the tired forearms thing was probably you learning to let the knife do the work after you stopped fighting a ragged edge, not the rod itself.