Those minions are nasty since they can hit the ENTIRE battlefield with 10 points of "true damage" (bypasses defense) in a single cast.

The only option is to basically nuke them from orbit as soon as you see them.  Even if it means ignoring juice AoE damage to just take out one of them since your sovereign and champions are fodder for this kind of nonsense.

I find this to be one of the weaknesses and imbalances in the game. The leveling up of your sov and his HP. The only ay to add HP to your soverign is to spend points on constitution when he levels. Now being a magic user naturally those point need to go towards INT and Essence to make the spells even worth while in the beginning. So, at least in most of my games, my sov is trying to increase his spell power so he can be useful in battle but it leaves him exposed as bascially a one shot kill when hit with even the most basic offensvie spell.  The only positive seems to be the fact that the AI in general isn't smart enough to target him. I just finished a games yesterday, a long one, where i faced a number of creatures that had offensive spells capable of 30, 40, or even 50 or more damage, and when i won the game my soverign only had a max of 15.5 HP with bonuses??? LOL..they never targeted him.

I'm sure this will get addressed as they improve the AI so something will have to change. I think leveling of heroes and soverigns need to give an automatic bump to constitution or HP. Right now you do not get enough points when you lvl to spread between INT and constitution. if you try to keep up with both before long your HP still isnt great but your spells are extremely weak compaired to the foes you are facing

First two things I level is their combat speed, not move, and their health.  Then I go after magic and strength.

I tried that encounter again and was indeed able to nuke the l'il devil down with fireballs before he could cause any mischief, thanks for the tip.

After that I thought I was in for an epic struggle, me with a ~1000 point army, and my last AI opponent having lots more territory and cities, but a bit behind militarily... but then AI committed suicide by attacking my main force with a sad bunch of soldiers and his sovereign.

The sovereign had some crazy defense, but in the end didn't last too long when surrounded by 6 units of royal guard with big heavy maces

Daft thing for the AI to do, maybe that needs tweaking, or maybe it was because it was on numpty difficulty level = poor AI judgement?

All of my settlements seemed to have maxed out as well, not much growth occurring - it wasn't apparent to me whether they'd reached some natural limit or whether there was some important stage in developing them or acquiring more food that I hadn't done.

Still, very interesting for a second game!

Best way to fight these is squads of troops with a couple levels. An unit of 4 will have 20 hitpoints initially, but level it a couple times and their hp's are in the 60's.

But if you don't have those yet and need help fast, use decoys. Simply take one weak guy out of your army and use him to attack the enemy stack. The vigilant minion will blow his arcane doom to kill a single peasant. After you 'lose' the battle, attack with main stack, the minion will be out of mana by then.