The point was, deathless runs. I consider Normal mode the 'canonical' difficulty I guess. There's parts in the games where even on Normal it's a bitch to finish without dying once.
Bungie considers Heroic to be the cannon difficulty, but the hardest game to finish on Legendary by yourself in my opinion is Halo 2 thanks to broken Jackal snipers and Elites whose plasma rifles fire 10x faster than your own.