Keep in mind Thorn has poisen that stacks 5 times and ticks 4 or 5 times each. In PVP without the buff that means the poison does 40-50 damage, with the buff that gives potentially infinite ammo that damage is raised to 7 per tick adding up to 112-140 damage not including the damage of Thorn's shots adding a potential 136 on the first 2 shots. Monarque does more poison, but only stacks 2 times, if you're in a rift you'll probably one shot wigh it. In PVP I would prefer Monarque because of it's longer range and AOE poison and 150 HCs sucking on console, but I prefer Thorn in PVE because of it's higher potential dps and ammo economy.
I'm talking PvP. Even powered up the DoT is pathetic. It's not an actual threat in PvP.
There's no denying Thorn's poison is shit without Soul Devourer, but there's not much they could do with it. D1 Y1 Thorn was OP as well as a crutch for p****** who couldn't play in a way that required skill and Y2 was useless out of PVE. Current Thorn though give us a better Thorn than before if you can manage the recoil and bloom. Without SD it's really there just for tracking and preventing regen.
Except the Dot lasts for about 1.5 seconds so it's not useful for either of those things.