What I really like about DAM is that a mage's powers are considered to be from an external source - God, Allah, Odin, Hecate etc. This is practically the opposite of Mage The Ascension wherein the metaphysic of magic is considered to come from one's inner self. You can see the medieval mentality portrayed long before the ideas of the self, ego, modern psychology. I think that each Fellowship having only 4 pillars of magic is a great focus and neatly delineates the limits of a fellowship's magical possibilities. Very underrated entry in the Dark Ages series. I am hoping to run a chronicle set in King Roger's Sicily : the cultural mix of Byzantine, Greek, Catholic & Arab is a heady brew!
While the order hermes was the main mage organization in Europe, and looked down on other factions and termed them hedge mages. the other factions were also powerful in their own way.
I have a different thought about the Valdaermen not being part of the Old Faith. What seems to me is that the Old Faith as a whole represent the conventional and acceptable beliefs and practices of the various surviving pagan traditions, and maybe that could even include whatever conventional Norse religious specialists might have been around (I think that's still a bit of an academic debate). The Valdaermen are presented as much more of a deviant Fellowship within their home culture, as well as not playing well with others, so it's easy for me to believe that they and the Old Faith simply want nothing to do with each other.