Thanks for the advice. I generally don't put my heroes in the same army, since the experience points you get from battles is less than what you get when there is only one hero.

Beat it last night. My army had a power rating of 2000, though. I had a storm dragon after conquering a Wildland, which helps, plus 3 cavalry, 2 bow masters, and 2 champions. Oh, and a level 19 Air Elemental.

Bring 4 companies of ice mages brimming to the hilt with ice damage, and max out their initiative and spell resistance (if you've gotten them up a few levels to have good HP, all the better). Use heroes to slow waelorga and haste the mages. Occupy him anyway you can. The ice mages will kill him for sure if given 2-3 shots each.

Melee units are nearly useless against him, but might get his attention away from casting despair. In my experience, he likes to attack adjacent sovereigns over casting despair. 

I don't know how practical this is but...in games in which the Master Quest is not a victory condition, could the map generator replace the pit of lost voices with some other wildland for more variety?

What if the "master quest" was either the dragon statues OR the pit of lost voices, but no game would have both?

Even better, you're right.