My memory had this dropping way more often back in the day. I figured I'd do a little digging.
One of the best resources back then for the mage epic was Matt Waggoner's Epic Guides:
https://web.archive.org/web/20011005...ofmastery.html
This source shows that he put it at 30%, and kept that assessment until the 2003 Hate Revamp 3.0.
Now Zam back then also lists his drop rate significantly higher
https://everquest.allakhazam.com/db/...3&p=2#comments
We have estimates of 1/5,
The one notable thing missing from the magi, staff, and epic pages on zam are that there is no one despairing about the earth staff really like you see on here, which leads me to believe that the 30% claim is at least within the correct ballpark. There is much more consternation about Quillmane.
Now as for data from Gravity, we have seen a rate of about 14% since 2023. Fuse has been less lucky (though their data might not be complete, since they don't use a website and I had a friend manually check discord posts, and was only from 2025), for a combined 10%.