Never underestimate the tactical use of mountains against powerfull AI enemies, it's what allow you to defeat armies that would annihilate easily your troops in plain/small hill terrain (assuming you're not playing with lowered damage to give you easy survival chance).
Playing the latest Pendor 3.51 it's not rare to run into much more powerfull armies than yours.
(Pendor increase the difficulty by making lots of unique high end troops running around while having insanely high stats and strong armor/weapons, trampling then over your regular non-unique troops that have much lower stats and equipment)
And the best way to deal with these situations is to lead your opponents into a mountain area to have the battle occuring with high elevations.
Recently i ran into a "Aventura Conquistadores" while being an Empire new lord , it was an army of 75 powerhouses that would have killed my 76 troops of mixed Empire crossbowmen and lots of various mounted merc (some high end level but still able to die by against those unique troops power units) very surely if i attacked on plains or small hills terrain.
So i "attracted" them (as in Pendor it looks like every unique armies running around are only attracted to you, it sadly kills a lot of immersion to me to see them ignoring every armies around them to go only after my troops) to a mountain zone and trigged the battle there.
Spawned near a very high elevation and ordered every horse guys to dismount, then with my whole army following me, we started to climb.
Soon the Aventura Conquistadores powerhouses started to charge , and were stopped in their track by the mountain that they had to climb very slowly, while i had all my crossbowmen lined on higher ground , with the whole infantry+dismounted horsemen, i made "blobs" of defensive shield wall to prevent the enemy to climb up to the 35 crossbowmen lined there.
And what a massacre it was, the 35 empire crossbowmen were'nt the higher end of the Empire crossbow troop tree , but at such a small distance, we crushed the whole Aventura Conquistadores with relative ease, and got only a dozen of losses in my defensive walls (and half survived thanks to my medic companion guy skill) .
So in all mode, all those pesky superubertroops, get an army of half ranged units + enough infantry+cavalry dismounted to create defensive wall, and lead the superubertroops into mountains, and see the surprise in the face of the "i'll easily walk on your corpse in plains" AI enemy
A variation of this is to have a terrain generated with a river, get your defensive wall in the river (as it breaks the enemy charge) and your ranged units on the side of the river.
It's more difficult than using mountains though (as the river may spawn too far from you to place your troops before it's too late) and the enemy AI, depending on their numbers can still overwhelm you from many side quickly.