How to Defeat Pale Ones with Troll King
First, Orm and especially Linnorms have pretty good magic resistance, which is what helps against mind blasts. If you can mass those, you might be able to deal with the olm armies. They certainly should do a lot better than trolls.
Second, Carrion Beasts, Stalkers and Manikin are all mindless, which means mind blasts don’t work at all. Meaning during an ambush of Carrion Stalkers Olms can only defend themself with fists. Depends on how much forests are on the map, but putting down a lot of Troll Forests might be worth it. Mushrooms also don’t get blasted.
Third, go for the citadels. Get every giant you can get your hands on and make a siege stack. Then avoid any field armies and just bombard the citadels. Should be easy to dance around the field armies as giant creatures can move fast through rough terrain and Olms are slow.
Fourth, get Gramps. Enable Earthquake on Gramps. Put Gramps in an army with a ton of trolls or chaff. Enough to stop the Olms from targeting Gramps until he killed them all by stomping really hard.