It's true that the deth metal knights are a major difficulty spike, but when you *fight* them it's a matter of having tanks and magic at hand to crowd control them. And assuming you already breezed through the game before them, you can handle them just fine. Though they are challenging they are not difficult. Dispel immunity = kill.
The entire game combat is basically a "first strike - crowd control - tank - second strike" sequence.
First strike because apart from VERY few situations, PLAYERS initiate the when and how of combat.
Crowd control because after that, your only goal is to survive until you can cast again.
Tank because if crowd control fails, your mages die with 2 hits in the early game
Second strike to mop-up whatever survived tanking phase
This is how AP/INITIATIVE combat systems always turn out. And why I hate them with a passion ;P AP alone "round" vs "round", but not Initiative based.... ;/
the AI is not really the problem. The AI CAN NOT counter a first-strike that happens "out" of combat. This imbalances the *entire* end-game where most fights are over before the combat round even *starts* especially when you have 2 meteors and 2 ice hails. The dependency on special attacks is indeed an AI problem but really, the player does the same. Tell me who starts their first round *without* a massive spell attack? In DnD You'd never waste a fireball or magic missile on goblins. Because they were preciously limited and you only had a few casts of them before you had to rest.
But with infinite mana + cooldowns, there is no reason to hold back. You should ALWAYS cast your biggest spells first, because the cool-down starts earlier, and you can cast it sooner again. Which is why the combat system is so easy and broken in a way. It's not the AI's fault.
The AI has to work with the same limitations, and so using special abilities early is the correct answer. Cooldown starts earlier, allowing you to use them potentially again earlier than the enemy (especially when you have Initiative advantage)