I've seen and tried 3 different strats this month (didn't play it back then), and tbh I had the smoothest runs with a tank-less comp while killing the Ahriman first lol. I didn't even think that was a VD run when we tried this comp (coming from the NIN or tank strats).
Team composition:
DRG(sweeper) & RDM mvp + DD COR BRD WHM
I guess DRG can be replaced by any other reliable Stunner, but at least whenever DRG is not stunning it can still deal high damage.
DRG (stunner + dd) - Focus on stunlocking dangerous targets such as the Ahriman at the start while DD/BRD/COR zerg it dowwn. Same thing with the most dangerous Fomors like Excalibur if you wanna just zerg it.
DD - Assist killing whatever tarrget is focused by the DRG/stunner
COR - Chaos/Sam ofc and act as DD assisting DRG's target
BRD - Can sing nq songs then NiTro Horde Lullaby the pack once the RDM brings them in, DDassit with others once all are asleep.
WHM - Cureskin the RDM before pull (the WHM wasn't doing it but it's ideal), Accession > Blink for Excalibur to make things even safer although shouldn't be needed. If RDM sucks and won't Silence the spellcasters (or if u don't have a RDM in un party), use Barthundra and Barsleepra to counter Shock Spikes and Sleepgas, keep Sublimation on.
RDM - The real MVP of the fight probably, as having a RDM with enfeebling potency BiS or close to BiS will make the whole battle smooth and safer. Keep Haste II/Phalanx II on basically everyone, Refresh III WHM and Enfire or En-day urself. Get into aggro range to pull NMs towards the start, keep shadows up with /NIN if needed and once BRD lullaby is done, you'll pop Saboteur and start crippling all NMs with specific priorities:
Alternate Para II/Slow (( casts on most dangerous Fomors, prioritize the Ahriman first with Para/Slow (should be enough), you could also Dia and Addle but Saboteur window is limited and the Ahriman will melt anyway while stunlocked.
Your goal as RDM in this fight is to remain ahead of your DDs enfeebling NMs while they're asleep before they get engaged, so you'll wanna prioritize Silence on Claustrum/Apocalypse/Mjolnir/Excalibur, Para/Slow on DRG WAR MNK etc, Distract III on THF (MNK / NIN good candidates as well), Addle for BST (but prob para/slow it's enough, both Silence/Addle won't really matter if they are stunlocked properly, they're just nice to have in case, specially Silence). Once key debuffs are up on relevant NMs, you can switch to DD mode, so your job will become casting Dia III on the focused Fomor while zerging them.
Ideally by the time you finish to put key enfeebles on all NMs, Sabo will be off since 15-30 seconds and you'll just go braindead DD mode focusing whoever the DRG is focusing.
If Excalibur will Invincible out of stunlock, you can switch to Crocea/su4 to keep damage going while shadowtanking it.
Stunner DD + RDM debuffs is what made this fight a breeze, BRD could also help trying Elegy to most dangerous NMs, but that's probably overkill.