I can't speak on Xionism in the past given I wasn't there, but in its modern state, Xionism provides a very sensible system of beliefs for dark mages and dark-magic aligned peoples. It serves as a great narrative-driving force that guides the actions of either individual mages or covens in their entirety, with differing moves being made by individuals who follow the different paths (i.e nameless, embers, etc). Xionism also does a great job of tying into server lore, too, with one of its main selling points being the hellish conditions offered by the Ebrietaes and the exploitation of the soulstream by the Aengudaemonica.
This occured, and still occurs, as a facet of the concept of Xionism, as the philosophy preaches complete disconnection from the Aengudaemonica and the exaltation of Man. It's completely open to interpretation by the player roleplaying it. You did a good job.
I can't really name a negative trait of Xionism, bar for lazy, poor quality "we kill god" roleplay that sometimes occurs; though, that's inevitable for any faith or philosophy on the server.