As a payer, I find this rule rubs me the wrong way, and so I either take a level as Dragon sorcerer, or Magic Initiate and get Mage Armor, or be a Lizardfolk and have natural armor. I think it's a terrible rule, but I like playing RAW, and so I find workarounds.
As a DM, my houserule is that Druids can use Padded, Leather, Studded Leather, and Hide (I don't worry about the studs, since metal weapons are okay), but if you have proficiency from some other source (being a mountain dwarf, a level of Fighter), then you can use metal armor no problem.
As a DM, my houserule is that Druids can use Padded, Leather, Studded Leather, and Hide (I don't worry about the studs, since metal weapons are okay), but if you have proficiency from some other source (being a mountain dwarf, a level of Fighter), then you can use metal armor no problem.