Poked through some of the old patch notes on Allakhazam, the best evidence I could find for this comes from here:
http://everquest.allakhazam.com/hist...es-2002-1.html
Scroll down to the bottom to find it (June 12th, 2002)
For the lazy...
** NPC Spell Caster Changes **
- NPCs are now bound by spell casting distance rules, meaning that an
NPC's spell will no longer connect from halfway across the zone
- NPCs now have a chance to be interrupted by normal combat when
casting newer spells
- NPCs that are much lower level than their target have had their
potential casting damage reduced using a similar mechanic to the one
that player characters' level differences use
- NPC Wizards no longer have an inherent bonus to their fire and cold
based spells
- Most NPCs that had previously had their spellcasting level inflated
to make up for poor spell selection have been brought back into line
with their actual level
- NPCs no longer automatically get free access to rarely dropped
spells, such as Garrison's Superior Sundering and Funeral Pyre of
Kelador.
Bolded what I think is the key part. They were stronger spell casters, just retarded in their choice of spells.