I know this is a little late but according to lore, guardians are some of the strongest fictional characters. There's either a weapon or grimoire that says if The Guardian (the player's character) and Ikora fought on Mars, it would knock the planet out of orbit and destroy it. Guardians also can only be killed by "Para causal" weapons. Basically, in order to kill a Guardian, you have to hit them and their ghost with a weapon that makes it so that their very existence in the current time is a paradox. Also, in the lore, subclasses aren't a thing. In lore, Guardians the use the light in anyway they want, the creativity of the Guardian is the limiting factor. They are basically immortal, stronger Green Lanterns. Not to mention what the Guardians face. The Vex control time and its flow. The ascended Hive are literal reality bending gods. The Cabal are 800lbs super soldiers and the Fallen are a species that the Traveler improved.