Ideal set for Dreams and Nightmares
As far as I have seen, this set works great.
All of them could work better at Level 5 or more.
Ancient Plate Set.
Savage Tortoise.
Obsidian Carbine.
Polaris. (Optional)
Ash of Agni. (This is the ONLY weapon you might need to do this run.)
Dark Retribution. (Optional)
Swift Steps II Perk.
This combination works awesome for the mission, and to farm radiant fire crystals.

I run
Cat pet *those heart drops*
Chaos Armour
Volcanic Plate Shield
Polaris
and Obsidian Edge
You can run many similar things even with better results but since I can beat it with no deaths i don't need anything else
Ash of Agni leaves you vulnerable to slime spikes if you spam it. When you spam polaris you can block any time as long as you don't do all 3 hits and have to reload. Obsidian Edge or Archeron is good to swiftly execute the gremlins.

Sorry. I thought that you had three non-optional weapons listed. Never mind.

I mean if you have access to everything you can make a much better loadout. Personally I run-
Black kat set (+ sprite msi perk)
2x pentas
Valiance
Dark retribution
Dark briar barrage
The big secret is that while fire+shadow is an optimal setup for the level, the waves themselves in dan are all weak to either piercing or shadow except for the very last wave which is neutral to piercing.
This loadout has the advantages of faster running, faster damage, all around cleanup, you know. The big tradeoffs are less normal defense which comes into play from the turrets, less health, and weakness to poison which isn't trivial although can often be avoided by just dying. Overall though I'd recommend the speedy route over the slower route, simply because it's not that big of a difference defensively due to specialized hits and speed is generally speaking what you're going for.
I agree that the Valiance and Dark Retribution would be great weapons, but piercing would be, in my opinion, not quite useful, because there would be 2 strong enemies against piercing and only 1 weak against it, if we look in that way. It's time consuming to use each bomb in turns for the same level.
I think carbine could be a good substitute for Valiance, it's better for breaking blocks and making way out.
As for Polaris, Gremlins and Beasts would be a challenge. I would rather recommend a Permafroster AND Ash of Agni.. Only 1 monster is strong against Shadow.
Also, although Black Kat Set is an epic set for this, but honestly, let's talk of affordability.. Let's rule that out.. Moreover, what about those who have a sick latency, over 250 ms? It's not quite easy to dodge.
I usually don't choose for swords, at least where these nutty slime spike release and turrets attack so frequently.
I strongly recommend Ancient Plate Set due to the seriously heavy defense against the Void turrets, it's a huge problem. Ancient equipped (Level 5) and the turrets will take out ONLY 3.25 HP each time.
Swift Steps would, also compensate it's MSD Medium.
I agree that the Strict normal defence would leave you vulnerable to Piercing based spikes, and Gremlin's elemental attacks... But the turrets seem to dominate over the other 2. But you always have the ultimate Dragon Scale Shield or the Savage Tortoise.

I think the appeal of running with a DBB is that it's neutral (or better) to both types of enemies in certain waves, as opposed to it being strong to beasts alone. It works well to wipe put the zombie/wolver and zombie/gremilin waves. I personally use it to finish off several enemies at once, when they're low on health from AoA, specifically the masses of gremilins that clutter at the bottom of the stage.
There's also the high flinch rate the DBB gets at a high damage bonus with gremilins, so I prefer it over the Dark Retribution.
That being said, you have a nice loadout put together. Never thought of using Ancient; I think a lot of people tend to find offensive boosts and MSI more useful most of the time, and I'm no exception to this. I find it much faster and easier to use glass cannon armor and slap on some pendants.

I use polaris + umbra driver. I'll use a swifty as my shield because it is the best. For the first two levels I use a msi perk but switch it to asi/damage for the arena as I don't really need to get anywhere quickly. As for armor just go with a set with good buffs for guns, I use a bk set but sometimes sub in more tanky armor with a BKC, but chaos, shadowsun, and the multitude of gunner update armors will work fine.
The most annoying enemies are the wolvers only because they are so hard to hit. If I had a mixer I would use it instead of the polaris. Gunning is an easy strategy and you won't have to die much.
This strategy is mostly for solos as you can keep track of all the enemies and not have to worry too much about the void slimes.
When I farmed DaN, my setup was:
(all weps are pretty much max DMG/CTR/ASI)
BKset gm defense so i can tank alot of hits :t
swiftbuckler shield
pentas x2
1.acheron
2.riftlocker
3.dark retri
4.mixer *for more dps you could probably run an orbit gun, or a cheaper version would be wildfire if properly uv'd.
drakon pet with msi med perk, spamming backfire barrier throughout the level, spamming frenzied firestorm for that ATK dmg bonus during arenas.
this was the fastest setup i could find during the time i farmed DaN. i tried many others with my gear but couldnt really find anything faster than my setup. i would rarely die due to mobs dying too fast lol.
Rift for switches/wolvers
dark to clear gremlins really fast
mixer would come in after clearing gremlins
acheron for anything that gets in your face.

I use the following:
Chaos Set
Scaling Hot Cocoa
Phantamos
Swiftstrike
I used to use Valiance over Phantamos, but reminded myself that there are no Fiend swarm monsters.
Thanks for sharing. We have lots of threads on this topic, but discussing it some more is okay.
Question: If you had to reduce your loadout to just two weapons, which two would you pick?