In a sense. Much of their magic was lost in the destruction of Netheril, and while bits and pieces have been found, a good deal of it is no longer even possible. Mystra, the goddess of magic, places limits on mortal spells that can be cast because of that event, and Karsus's actions in it in particular.

Karsus once attempted to become a god, through a great spell cast to sap the power from Mystryl - Mystra's former self - and only succeeded in almost destroying the Weave, killing Mystryl, and then turning himself to stone. A classic tale of wizarding hubris if there ever was one.

Even so, he was a great mind.