Merciless (Solar Fusion Rifle)
Fusion rifles, in general, are always a really solid option in Destiny 2. They do really great damage, have relatively decent range, and normally have manageable stability. However, this particular exotic fusion rifle has an interesting perk that makes it one of the best single-target damage weapons in the entire game.
Merciless’ intrinsic perk is called Conserve Momentum and it allows for the weapon to fire faster each time your shot doesn’t kill the target. That lets it absolutely burn through majors and any boss enemies you come across, especially if more than one person on your fireteam has a Merciless on them. With the enemies in the Leviathan Raid being quite tough, this will definitely help cut swathes through the crowds.