@ Babby. Thanks - I kinda thought having a dragon or two would have easily tipped the scales. Unfortunately I had only *just* found and defeated my first dragon lair, so was still trying to research dances. A dragon or two would have probably beaten him up and taken his lunch money...
Can I be honest? With 205 HP and 50 def... he won't even survive the opening salvo against my chargers. I don't understand how he's eating your stacks.
Legitimate question. I probably overstated the "death stack" part in the OP, although they had been pretty deadly agains everything ELSE they had run into. I had been playing a pretty lazy game (fighting a desultory two-front defensive war while my sov ran around clearing wildlands) up to that point (challenging/challenging, large map, dense monsters/wildlands, 4 factions only). Makes for a longer game and I wanted to try out a new sov build without being bothered by the AI (*except monsters). Soooo, anyway, in spite of the game length (and remember I mentioned I'd wasted ~20% of the game chasing stupid syndicate armies around my core area), nothing was really super far along development wise. If I remember correctly, I had three hero stacks of 7 units, with 5's unit sizes. I can't remember the exact mix, but it was probably my "default" of an ice mage, a fire mage, an archer, three hvy cav and hero. All mounted, custom designs. The computer classed each stack as "deadly" (and we all know how accurate THAT is...). I used the spell that brings everybody to a tile (Call of Titans?). After all, didn't look too tough, right? Ate my Sov, sent in the back up. Ate that. Retreated remaining group to nearest city. Won battle on auto-resolve.
In any event, I think some of the suggestions about spell use/mix was legit. And btw, I used a similar stack at a similar dev level to take out Ruin of Summer without even breaking a sweat - and he has 500 hp and about the same armor. Blizzard scrolls are your friend on that one 