False damage, not decay!!

For storming vs AI I've found putting most of the troops far back on 'hold and X' orders can work well. That generally means the AI troops will exit the fort and get surrounded by your troops. You can still get trapped up on the fort walls a bit, but it's better than fighting directly on the gate where you can only get at a few enemies at a time.

if we assume you have an opponent who can strongly block the gate, then getting quality archers is actually pretty legit. You have a bunch of undead commanders with nothing to do. Pop your bow of botulf and some other bows on them and use the nature precision buff and they will kill quite well. Position your undead chaff with guard commander on the far flanks so they kill any wolves coming in, don't want your archers and mages getting distracted by them. In sustained fort battles I use the 5 nature gems 0 encumbrance shield for casters. Shield encumberance counts double for fatigue, but the 0 ones don't add anything. That way you can have sustained, long term casting. Sustained battle casters like these you don't actually cast fatigue heavy spells, you use their high ability to spam cheaper spells that they can somewhat sustain the fatigue of. Eye shield and weightless shield is also 0 encumberance at low construction. In dom 6 you don't have to wait for breath of dragon for a damaging ranged aoe nature spell, there's the venom darts you can use too. 10 turns of venom darts will be pretty mean. You argue that the longbow centaurs are too expensive, but I think throwing those Pan thugs in is a lot more expensive. You shouldn't be getting 100 of them anyway, just need enough for a stack so they don't rout, maybe 30. 750 extra gold is not much if it means getting a capital. It's also not much compared to throwing 600 of your undead troops into their banishment graves. With this kind of build you only need one champion to duel the Mother of monsters and the problem of the fight is solved. Ranged damage+thug should overwhelm her regeneration fairly easily.

Forgive me if I'm particularly stupid (never played Dom myself) but couldn't you have stormed the fort by sticking 10+ elephants at the front of your army, told them to attack immediately, and then stacked your other troops from slowest to fastest (front to back) and position their blocks as far back as possible so that your elephant/behemoths smash the choke point while keeping the rest of your forces out of grind for as long as possible?

I think it's not a bad thing that it's hard to take a Capital with hundreds of units in it, even from the AI, with 15 mages inside when you're hardly bringing mages of your own; they're all hanging out in labs. I suspect there's a bunch of things one could do involving gems and mages; whether it be Panic/Terror spam, your own Howl, skellyspam, Shadow Bolt/Blast, illusion spam, summoned Wights or Shade Beasts, etc., that could help with storming a capital; but I think against the AI there's always the temptation to not respect their armies with a real mage commitment :). I'm pretty sure you can just preach a bit and watch Pan be domkilled by the other players' temple spam though :)

i find you get a lot more use out of the manikins if you split them into groups depending on type: manikins, satyrs, harpys and boars can all go in one (main thing to look at is speed and importance of the troop type), all the extra special ones into one like bears and ogres, with maybe elephants in their own, boars can also be useful on their own with hold and attack closest in front of your horses/wolves (who should be together) who should be on hold attack rear (hold is always optional depending on the info you already know between the difference between holding and not, at your digression). sacreds is actually less important in this regard, its up to your preferences but i try to save them up til i have a critical mass of them, and using some of the bowers to seed enemy troops

Just need the enchantment discount site now for the Hinnom trio.

19:00 Could you not look at the log for your thugs to see what hit them? Did you consider a scary helmet?

nest of asps i believe might be the culprit here 16:47

Once you get your own conj 5 casting howl before them becomes an option at least. Too bad they only spawn outside the walls.

Could you put elephants on guard commander on your flying thugs and spam the fly spell? That should allow the thugs to really do some damage on the back lines