Apparently I failed my search-fu.
My only question after reviewing the reason why the original suggestion was denied;
Isn't Bronze weaker and heavier than Iron? So, shouldn't it be slower and easier to break?
IMO Bronze would fit well between stone and iron.
Perhaps diamonds could be macerated into diamond dust, then one combines a diamond dust with iron, creating Adamant. I envision 1 diamond dust + 2 iron = 4 Adamant.
Adamant tools could be another option for a step up from iron, besides, bronze being better than iron just seems silly.
And if all of this is simply out of the question, just say so and I'll shut up about it.