The final release of Unangband 0.6.4 will be a much kinder game. This is due to the generous contribution of bigalphillips, fixing a bug that caused spell damage to be grossly over the intended amounts.
I was referencing the wrong field in the monster_race structure when computing the actual spell damage inflicted.
As Al puts it:
Apprentice mages used to use a power of 9 instead of the spell_power of 1 for their spells, causing the major damage.
This makes many dungeon guardians much easier eg. The Dunlending Agent has a power of 28 but a spell_power of only 8, so he'll do about ~third less damage now. :(
I also want to thank Big Al for picking up and fixing so many bugs this week...
[Edit: For those concerned, damage from breath weapons is unaffected].