[Micah]

You misunderstand, the big gun spells wouldn't be used to take down the domes, just to get one cast through (taking the dome out is incidental at that point). If your opponent has a pile of mages/boosters in a single province it can be well worth it to suck up the gem cost to lob in 5 flames from the sky. It will leave you far, far ahead in terms of economic damage. Taking out just 3 tart-casting liches (skullface, ring of sorcery, and skull staff) is 155 gems worth of gear in S and D gems (after hammers). 3 Flames from the Sky is 175 F gems, which is already a worthwhile trade. If there is a pile of mages with dwarven hammers and other boosters forging away as well you're going to clearly come out ahead.