Why do all late game recipes use iron? They don't. You're actually just complaining about padded armor. Mistlands-tier armor does not use iron. Plains-tier weapons do not use iron. Most mistlands-tier weapons don't use iron. And, of course, no food recipes use iron.

The best use for blackmetal is blackmetal chests, though. The storage capacity and aesthetic value of them is great.

That said, iron is incredibly valuable in this game. I consider gold and gems to be trash next to iron. That's mostly because of how useful it is in construction, though.