Sub-optimal compared to what, though? No one wears metal armor on Athas, so the non-metal armors become the baseline. If a suit of metal armor was discovered in some ruins, it would be turned into something that Athasians could actually use.I can see why Metal armor is a bad idea. I've been in the desert and have seen the results of overheating far too many times. That said, the bone/horn/whatever armor is supposed to be sub-optimal materials.