Caster druids can still wild shape as many times as Moon Druids.That's just your perceived balance, and even then its for Moon Druids only. What about the caster druids? They got no Mage armor/Shield, no Shield of Faith, and they can't cast spells in wild shape.
Then there's the stupidity of having proficiency in Medium armour, but can't use any of them bar Hide because they are all metal. Why not just remove it all and leave Light armour?
At second level, if they turn into wolves, they get two sets of 11 hit points. Which means total hit points (assuming Con 14), 17+11+11= 39 hit points. Which is equivalent to a 3rd or 4th level fighter. Which is pretty good for a non-tank character.
I'd say if you want druids to have AC equivalent to metal armors, they should be given the option to quest for scales of certain creatures (dragons or wyverns or such).
Give a role-playing or in campaign incentive that creates more adventure.