Just my take on this weapon given what I've observed. Gjallarhorn as we know it is the strongest weapon in the game. It's a rocket launcher that tracks with a large explosion followed by Wolfpack rounds that try to finish off whatever the explosion didn't. The Weapon itself was created after the battle for Twilight Gap, one of the largest battles in defense of the City. This is perhaps why the weapon is the strongest in the game as it is a bit of a sacred item within the Lore. It was created using armor from Guardians who died during the battle. Wolfpack rounds represent the "Strength of the Wolf" which is displayed in the crucible medal when your team takes out ten guardians without losing anyone from your team so it shows teamwork to overcome the odds. The weapon is a symbol of humanities strength to not only fight back against the darkness but to overcome it. It is the weapon that can cripple Crota and it can outright destroy Atheon. Who knows what its role will be in the house of wolves but so far the Strength of the Wolf overcomes all. So while a single Guardian with the Gjallarhorn seems like a one man army in reality he's not. With the strength of the wolf that single guardian with the help of all those who fought at the battle of Twilight Gap destroy the enemies of the darkness. *Sorry if this topic has been made before I had not seen too much on it since reading the forums for a bit*