Yeah. There's nothing unfair about the rules in KOTC2, what really makes the game so hard is that enemy AI is completely insane. No D&D game, possibly no turn-based RPG in general, has ever implemented enemy AI this good. In particular, enemy spellcasters are free to use all the spells they have, do so fairly intelligently, and really just go to town on you if you actually allow them to get casts off.
On a related note, in the difficulty explanations you quoted, one of the items is "enemy Negative Levels" (turned on in easy and normal). What that means is that in certain encounters, some enemies have been configured to get a -2 (or whatnot) level penalty. It usually gets applied to enemy casters to knock one level of spells off their repertoire - which ends up being fairly huge.