Sweet Business should have been in Destiny 1. It's that simple. It would have been a perfect match with the nightmare PvP meta that was imposed last February.
Simply put... the special ammo nerf, or the 2-14-17 Abomination as I like to call it, essentially did one thing. It essentially forced the player to have one, count it ONE reliable weapon. And the very nature of Destiny ensured that having only one weapon made you combat-inadequate. There were always things that your one weapon just didn't do well: an auto was weak at long range. Scouts got overwhelmed up close. While I had OK results with the SUROS Regime and PDX-45, there were always times when I needed a longer-ranged gun for far off, or something more potent for up close (or a bit of both, with Regime). It got so I had to start semi-maining stickies, Invective-camping, and eagerly awaiting Doubles playlists (when you could get enough special) just to remain, in my eyes, combat-effective.
But then, along comes Sweet Business. With its stability and its decent sight, it can puncture enemies at a surprising distance. And with its chainsaw ferocity at full spin, it kills as fast as anything in the game. Running it in PvP, I don't equip my energy gun. I let my teammates pick up the purple ammo, and give sweet business to enemies when they go for it. It's almost like having a machine gun again. And it occurs to my that if this gun was back in D1, with TTK adjusted of course, having only one working gun wouldn't be the handicap that it normally was.
Well, as always, your results may vary. I probably perform marginally better with my MIDA/Uriel combo, or the Vigilance/Last Hope combo my warlock uses. But it's just fun barging around the Crucible spewing an endless stream of death. When I use Sweet Business, it's generally all I use.