Well I spose you could say that light level is somewhat cannon however more so in a way of more time spent as a guardian = more time to practice bending the light and dark to your will to master already known abilities or create new ones. Now lore keepers please correct me if this is wrong but I also believe at some point in the lore Elsie Bray tells us the reason why she's keeping a close eye on us in the timeline of which D1 and D2 are set is because out of the thousands she's seen its the only when where we are the one/ a part of the group who defeat every major threat. This is the only timeline where we were there to kill atheon, crota, orxy, stop the Siva plague, defeat the red legion, defeat Riven and wield darkness without turning into a disciple. So I wouldn't say it's luck based most likely just that in all the multiverse there exists 1 instance of everyone at the absolute height of their power and that's the version of us we are playing