Crowning Duologue is one of only two Strand rocket launchers in Destiny 2, the other being Semiotician from last year's Season of the Witch. Since The Final Shape released, however, that weapon has become a lot harder to get, leaving you with few options if you're a new player looking for a Strand rocket launcher.
Crowning Duologue is also a Solstice weapon, meaning it's only available as part of this year's event. The good news, though, is that it received a perk rework alongside the other event weapons.