they wanted to use the new supers. they saw it would be more fluid to the fight and more room for thought since it can be thrown like a grenade. they made this. people like you who think this is relevant to the story watch it. then its officially cannon. their is no lore to who killed crota. their will never be. don't assume that if its in the trailer it is cannon. the first one had a hunter blink with a incendiary grenade. your argument is invalid.