I assume you haven't read anything written by Vance, because magicians in there are so much more like wizards, especially in the '70s, and arguably still today, than anything Gandalf ever did. Such as their continual quest to amass more spells and their memorizing of The Excellent Prismatic Spray.
If you read the books D&D lists as influences, it's pretty obvious where most of this stuff comes from.
Agreed. And not only the spells: magicians in Dying Earth (Vance) behave pretty much like the psychopathic murder-hobo trope of the D&D player stereotype.
Vance's magicians are childish, petty, reckless, vindictive and power hungry.
Hah yeah. I like to say that D&D has the soul of Vance with a coating of Tolkein. It's not 100% true as there's lots of influences, but as a DM reading that series made me think "this explains so much".
If you read the books D&D lists as influences, it's pretty obvious where most of this stuff comes from.