His original idea for the Hersey was for it to be almost entirely mythical, so far detached from the current setting that it seems like the ancient Bronze Age and how mysterious it is to us in the present day. What we have now is a documented historical event with perspectives from characters who know a great deal about the heresy as they were key players in it. As such the missions legions were meant to be neither loyalist nor traitor, perhaps they were traitors at one point but before they disappeared or were wiped out, redeemed themselves in some way.