There was some discussions on NPCs some time ago.
Some discussion concerning Aerie's specialization and other NPCs can be found here:
Obsolete URL removed I think there is some more threats on this, but I don't remember now.
I disagree though, the "weakness" of the diviner class depend fully on your playing style. I've never liked the conjuration spells. Accept for Melfs Acid Arrow, flame arrow and the better power words. The creatures you can summon are (in bg2) useless after SOA and then everyone gets to summon the planetars. The diviner is actually my favourite class when I go for a wizard.
I don't like conjuration spells either, only the spells you cited above.
I only said, in pen-and-paper D&D 3e, more powerful schools (ike Evocation and Conjuration) have more severe penalties than weaker schools (like Dination, Necromancy and Illusion). I'm not saying divination isn't a good specialization, especialy becouse you can chose any single school as a prohibited school.
I'm playing an extremly powerful Illusionist!
I think the prohibited schools for IWD2 specializations are too strange and most of them are too severe.
Sorry for the extense answer, but I wanted to clarify my pint.