Precursors are the creators of light. They can create and delete what they want across a multidimensional plane. They literally just have to think about deleting oryx from existence and he's gone. They can also alter time but are far more older than vex. The precursors have no real form even though they created forms for themselves. They are actually immortal. The only reason they were killed is because they allowed the forerunners to kill them so they can have power passed down to them until the precursors were supposed to return.