If Xenophage gets its damage increased against bosses by 50% it'd be the go to weapon for all activities except maybe the Sanctified Mind (depending on how bad the range penalty is). The only thing that'd beat it would be an Izanagi * 4 shot followed by Love & Death. All of these tests were done on Riven with a solo hunter without using any buff, debuff, or faster reload mod/ exotic. I did use the hunter dodge for the first reload where applicable (but I did find that it usually didn't change dps that much). Most of these weapons were tested on October 1st and then the exotics were tested as they came out.
Primary Ammo
Bad Ju-ju 55,000
Trinity Ghoul 58,000
Ace of Spades 65,000
Jade-R 70,000
Last Word 72,000
Graviton Lance 73,000
Sunshot 74,000 (didn't get a good run)
Skyburners zoom 75,000
Mida-multitool 77,000
Lumina 77,000
SUROS Spin up 81,000
Thorn 82,000
Crimson 83,000
Le Monarque 83,000
HardL nobounce 84,000
Fighting Lion 86,000
Vigilance Wing 88,000
Hush 100,000
Huckleberry 101,000
Wish Ender 109,000 (Bonus damage on Riven)
Polaris Lance 110,000
Rat King 120,000
Riskrunner perk 133,000
Cerebus +1 Cat 140,000
Sweet Business 145,000
Malfeasance 155,000 (Bonus damage on Riven)
Outbreak Perf 150,000
Cerebus + 1 162,000
Tarrabah 231,000
Sturm and Drang 369,000 (Yeah good luck with that in a 6 man group)
Special
Chaperone 101,000
Revoker 107,000
Prometheus 120,000
Wavesplitter 165,000 (4 second of perk)
Lord Wolf perk 168,000 (extremely close, possibly even higher on crit)
Arbalest 203,000
Izanagi mas/p 204,000 (possibly 250 if I got the last shot in)
Borealis perk 208,000
Eriana's Vow 222,000
Jotuun 226,000 (at least)
Cold Heart 229,000
Telesto 250,000
Merciless 287,000 (ran out of ammo)
Power
Tractor 21,000 (.....?)
Wardcliff 81,000
Worldline Zero 100,000 (died to corrosive aura)
Black Talon 150,000
Anarchy 168,000 (constantly shooting)
Acrius 175,000 (calculated out not demonstrated due to difficulty, 17,000 a shot)
D.A.R.C.I. 193,000
Queenbreaker Ma 233,000
Sleeper 242,000
Thunderlord 251,000
Leviathans's Br 267,000
21% Delerium 272,496
Deathbringer 270,000 (45,000 per rocket directly in mouth, 47,000 if you hit the ceiling)
Whisper 275,000 (probably closer to 300,000)
Xenophage 285,000
Colony 288,000 (ran out of ammo)
TwoTailed Fox 321,000
1k voices 339,000
Edge Transit 365,000 (with spike nades)
Prospector 383,000
Truth 388,000
Love & Death 423,000
Izanagi & L&D 469,000
Izanagi & Wend ~350,000
Bonus
Cluster bomb rocket. 54,000 / rocket
Celectial Nighthawk 227,000
Loaded question 37,000 / resovoir burst. 243,000 solo. Can get 10 shots
Luna's Howl 80,000
Not Forgotten 76,000
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Did you even look at your own numbers? -blam!-ing merciless does more damage than xenophage according to you. Even edge transzit does more damage. How would a 50% pve damage buff make it the go to option if there are better damage options?