In a game without iron or steel weapons, I'd be inclined to use damage and armour values as normal - just perhaps use the lower hardness mentioned in the DMG. It'd just be simpler than subtracting 1 from weapon damage all the time.
If bronze was the predominant metal and there were a very small number of REALLY GOOD ironsmiths - capable of producing steel - then steel could be a better material from which to make armour and weapons. Early ironwork wasn't necessarily much better than bronze - it was just a lot cheaper to make because, once you have the techniques to work it, iron is more common than copper and (particularly) tin.