I'd like to add my piece to the conversation. We were originally struggling with the fight when we tried it a few times in 2018. A lot of the information out there makes the fight "doable" but there's definitely an optimal way and here's the best we've found.
Setup: PLD, WHM, BRD, RDM, COR, WAR (Using R15 Chango)
Our clear time was 24 minutes.
Here's a few details from the clear:
1. RDM is now overpowered in the fight. You can debuff everything making sleeps easier to land, rendering the boss relatively non-dangerous. RDM can also build huge en-spell passive damage so it's worth having. Inundation is very strong on this fight.
2. BRD was meleeing with Naegling and taking part in skillchains to reduce the DT lockout for every part of the skillchain.
3. Our WAR was using Tomahawk on cooldown. Full Break / Armor Break was used sometimes, but admittedly I was not on top of it.
4. Our COR was strictly using a Leaden Salute setup and meleeing for TP.
5. Light carols. They literally made all damage trivial. LC1/LC2 and you will take basically no damage. At the start of the fight we stacked 10 bard buffs and let the outside bard do SV / CC Scherzo so we'd have it for 18 minutes of the 24 that we were fighting. That freed us up to run both carols for a very large portion of the fight and it made a 100% difference.
Now for the juicy bits. The entire fight consisted of the same strategy - make radiance, but the WAR is closing the last two steps and taking full advantage of Inundation's skillchain damage boost.
Our WS rotation was:
1. Leaden Salute - Always hit between 10~30k damage. (Veeeeery acceptable for the huge DT on the fight.)
2. Savage Blade (BRD or RDM if BRD was singing)
3. Upheaval for AM3 - SC always did between 30 and 50k damage alongside a 20-30k WS.
4. Ukko's Fury - Not much to say, Ukkos sucks, but radiance always did 10-20k dmg
Edit: The reason we use Ukkos here even though the damage is low is the ensure that that next Upheaval is full-damage and experiences no withering effect.
So the whole fight we're generally copious amounts of passive enspell, RDM is also using Sanguine Blade for 5-12k an avg, and then the SC damage is the main driver for the fight.
Our strategy progression was something like this:
Try what's said on BG Wiki - Our RUN kept getting bopped by SCs after her AoE wiped shadows.
Try killing adds - Lion is so annoying
Try just melee zerging - Damage is weak and DDs die somewhat frequently, fight takes too long and adds become unsleepable a little after the 30 minute mark.
Try going hardcore SC on adds - works somewhat, but we end up back at square 1 with "why are we fighting these, it's stupid"
SC zerg Iroha: Only need 2 sleeps so it minimizes RNG on Nitro resets and ensures you do not reach a full-resist state for sleep.
Our total attempt count was around 10~12, but I have not accurately tracked that information since we took a break for several months after attempting this the first couple times.
Here are some photos that recount damage details. This does NOT include the first phase of the fight (which was over in 3 minutes, the SC destroys her too).
Weapon Skill Stats
Total Damage
Clear Pic
All three hours of attempts were streamed and available as VOD here:
twitch.tv/shozodrg