The idea of Classes was created in the Last City to organize Guardians. Risen do not start with a Class (except in-game, because of game mechanics). After joining the Guardians of the Last City, they choose what faction to join based on their way of thinking, beliefs, interests, goals, and personality. Instantly being revived with a Class is a game mechanic, but its also slightly reasonable because the way a Guardian uses their Light reflects their mindset, though the way they use their Light is also learned from other Guardians. Really, use of the Light shouldn’t be so heavily Class-based, but game mechanics make it very rigid.