The Acceptable Breaks from Canon parts of the game are due to Steven being a Fisher King.
Because The Light is serving Steven, it is also creating the environment and even influencing the Gems' and Steven's powers; and in some cases personalities. Throughout the game, you play as the part of Rose Quartz who lives within Steven.
You "control" Steven himself, as well as the other Crystal Gems, by making choices that a leader would make. The player is actually playing as Rose Quartz, guiding Steven's decisions from within.