Virtually any scout rifle and hand cannon can spawn with Firefly. It's not unique.
The only thing wonderful about Fatebringer is the arc damage, which granted, is great for nightfalls and the like but otherwise unimportant.
Other hand cannons can have the same (or better) perks and the same (or better) stat blocks.
It's great that you like it but it's not as specials as everyone seems to treat it.
English
-
Had tons of HCs and SRs with firefly. FateBringer's is much more powerful. Other ones just seem to bump the guys around the exploding guy. FB kills everything around it with a red tag. It's not a unique perk but there is something in the equations behind the perk that cause it to be devastating and unique to FB.