Personally if I was dealing with someone who liked Flames from the Sky that much I'd just forge a ton of Fire plate or Rings of Fire resistance
Throw in some hammers and you can protect about 11 Mage's for the gems they spent on just one Flames from the Sky
If they were going to cast 6 of them thats about 66 mage's you could protect and the Plate would help against other stuff as well.