In terms of answering the question, Quest Pack is nowhere near as painful as most components of the Tactics mod. But it must be said that the various components of Tactics were written by many different authors, and even two components by the same designer are of wildly varying difficulty levels.
Weimer's take on things like Improved Irenicus: "What if Irenicus was more powerful than most gods, could cast an infinite amount of spells and prevent you from casting any spells of your own?"
Quest Pack's take on things like Improved Irenicus: "What if Jon wasn't such an idiot?"
As far as EXP is concerned, my own view of the subject is that when you kill any creature, the party is awared 1/2 of 1 percent of the EXP that that creature would have required to reach its current level (with modifiers for factors that affect difficulty in killing it, like being immune to weapons of X enchantment, whether it has a large amount of special abilities, etc). Kill a Level 12 Fighter, get 5,000 EXP.