I could see how prone would benefit players(especially on the moon in pvp) but destiny has a lot of Halo features in it, in case no one saw them, including the fallen(covenant), the hive( the flood) and the guardians(Spartans). It is because of these similarities that bungie has not put prone in the game due to the game bein like the little brother of halo... They need to keep in some classic stuff and prone was not one of them.