The problem is that after the initial undead fights, the game starts having too many priority targets. Using the bandit/pirate fight again. The two archers are priority because they have knock down, poison, fire arrow, stun arrow, and freeze arrow. All of those are issues. Then the melees are priorities because they pack crushing fist and are buffed from the battle mage who also has ways to stun you. All of the units here have the necessary CC to make them a priority target. This causes issues because no matter what you target, you're going to wish you targeted the others first.
Another example is the Evelyn fight. Evelyn will cast up to five spells in one turn, making her a high priority. The cyclops mage can cast up to three and has the standard mage skill book making it a high priority. Then there's the lieutenant who heals from fire, deals pure fire damage, and summons fire archers who have the same traits as him. This is made worse by the fact that the lieutenant will do 100+ damage even with fire resist potions on. So he's a big priority too. If you focus him, you'll have issues with cc, if you focus the casters you're going to have issues with big fire damage and adds that heal off the fire fields that will be on the ground.
There's just too many priority targets here, and the biggest reason is because the archers and mages have everything available to them. This cyclops mage can cast everything the undead mage can and everything Evelyn can, and all the things the cultists could. There's no variety, no change in how I'm going to deal with the mage. They've just added in the lieutenant who's more dangerous than the mage to give us a higher priority; but we get punished for choosing one either way because despite adding in this higher priority, it doesn't change the fact that a mage is going to cc the crap out of me if I don't take care of it.
