Rebalance armor so that all “mail” armor and most of the iron body armor in general is not useless. Ideally, the worst iron armor (orcish chain mail) should be considerably better than studded leather, but they are equivalent. The ideal balance, keeping leather armors and all weights constant and not accounting for to-hit or damage reduction, is probably something like the mails going up to 9 or 10 AC, and splint and plate getting up to around 14, but this is not possible to implement without changing the combat system.