It makes the wave sections a cakewalk and wave sections are the other half of this game. In fact, I'm certain FB shaves more time off for players than BH does. BH only useful against stationary bosses, FB useful anywhere from missions, patrols, non-boss strike sections, raid sections without bosses. Killing adds is a crucial component in every activity in the game and FB is quite easily the best primary in the game all-round allowing you to strut Gally as your exotic of choice. Plus it has arc burn and it is the most common modifier in the game thus increasing its usage even more. According to Bungie logic it should be nerfed. A team with only FB can breeze by every single wave section faster than teams without it!

Fatebringer doesn't shave off all that much time. It's just another handcannon, except it makes explosions to add a nice amount of dmg to the other adds. It's a really nice weapon, but not it's not absurdly above the rest, as are Gjallarhorn and black hammer

It has 4 of the best perks in the game pre-packaged. With how easy it is to land crits with HCs, proc on firefly and outlaw are virtually 100% per mag. That means it's basically a continuous source of DPS against mobs without the need to reload and look for cover (unless you took too much damage). You'd be surprised by how much time is saved from killing mobs. The Sepiks strike's biggest time waster is the wave section and not the walker or Sepiks encounter. That means you get to shave a lot more time off there if you can efficiently kill the adds in those 3 waves. With FB, you can clear that room in a couple of minutes without even using anything else. Hitting HS against any dreg will instantly cause a chain reaction that leads to easier kills against vandals and other dregs. The only faster way to clear them would be with dual shottie (Remote + shottie) but then you don't have Gally and a BH. With FB, you can forego a shotgun and just roll with a sniper for when the boss comes up. That is how OP FB is. There is no need for burst DPS against adds when FB will cap them and at the same time splash all enemies around for good damage. Meanwhile, BH is situationally good against bosses. Big deal. It is useless elsewhere and now it's about to become obsolete to every good sniper roll out there.