Warriors, rangers and scoundrels support physical damage, not magical damage. So they don't help that much with magic armor.
Necromancy is physical.
Not exactly so.
Mosquito Swarm cares about physical armour.
Infect deals the biggest damage to Magical armour you can do in this game at the moment. Hit them with that and then your Aero or Pyro of choice and you are golden.
Not sure about earth things. Poison and Earth seem a bit confused at the moment.
