I don’t think they were a thing in the actual 2e Planescape setting, or at least not a big thing. My copy of The Factol’s Manifesto, which really dives into both the philosophy behind and also the on-the-ground Sigilian politics of each of the major factions, doesn’t mention them. (It is a delightful book. HIGHLY recommended if you happen to see a copy in a used bookstore somewhere.)
Which, again, at least means that the Planar Handbook isn’t just crapping on interesting preexisting lore by saddling it with godawful mechanics (as the book is wont to do), but it does raise the question of exactly why the hell this class exists and what possible design goal it’s serving.
I fully expect some wonderful entries. I’m becoming less convinced that I’ll be a participant: my time over the next few days is getting very rapidly claimed, and there’s no way in hell I’ll get anything in once class starts back up on Monday. But stranger things have happened, I suppose.