Yes, the fire line are much overpowered, they make siege weapons useless... i actually don't even build any siege, as the level 3 fire apell is much better, they reduce 30% defense in a turn, have coletarel damage , can kill, cost no hammers, and have 100% escape (as they die and can be summoned every turn) , why would someone ever build siege with this? cost hammers that can be used to other things, get a slow movement unit, that cannot bebefic of any spell that afect living units (regenerate, hast, etc), and have a chace to be killed to cause colateral damage?
Maybe if siege got a 100% retreat, they could be even cosidered for use in the future.