There are big differences between the factions. For instance, the Oni of The Chosen can throw a throwing knife as a feat and call in fire arrows to rain down, which is an area of denial feat. The Warden of The Legions meanwhile can heal themselves as a feat and can call in a catapult which is a one and done huge explosion that will kill those within it's radius. Aside from feats the factions are also different fundamentally, The Legions have more armor, The Chosen are faster, and everyone's best guess is that The Warborn deal more damage. They also have different weapons that behave differently from their other factions' counterparts. So it's not just different looks that separate the factions.