Stone, Copper, Aluminum all better options than Iron for below Bronze

Though one other issue i have with Iron, is that Iron usually is a Silver color in almost any game you play, so i guess Copper / Aluminum would also kinda step on the color coordination.

But there are so many better materials below Bronze that would fit that are not "offensive" (reason they wont use wood apparently even though i think Bronze is about as offensive as you can get since wood looks nicer and is more useful)

Stone Rock (or pick a particular type of rock like Igneous, Sedimentary, Metamorphic or go a step further and pick even more specific) Brass Copper Aluminum Tin Wood

these are just examples of other types of metals / stones that would make more sense to be under bronze than iron