Bad Sortie Runs Are Bad, And So Can You!

The ability of the D/H Boss, indicates his offensive-mode or sometimes called "Absorbs Dark" or "Absorbs Light" mode in a defensive context. So, Fulminous Smash is offensively Thunder/Light-aligned, and will enable Degei/Aita will Absorb Light-based Elemental skillchains and magic. The correct response is to Nuke with the ascending element, Earth, which is Dark-aligned to proc/prevent an increasing Damage Taken-Minus effect on the D/H boss. (Keep in mind, in a magic strat, you would still do an Earth/Darkness-aligned skillchain like Gravitation > Darkness to deal damage effectively, on either D/H boss).

Here's the part where DDs get confused, and folks just expect to steam-roll over H boss and sometimes fail miserably: If you do a Weaponskill or Skillchain of an element that is a matching the element to his offensive mode, like Light/Thunder in the Fulminous Smash example, Degei/Aita will not only absorb the damage, but also spawn a fetter.

This is the cherry on top: The fetter will also have an associated debuff, that is aligned with it's own element as well. This is explained/quantified below.

[confirmed]: The spawned fetter is the same element of the ability the boss does, so Fulminous Smash is thunder-aligned, so you'll get a purple/Thunder fetter.

The debuff associated with the fetter matches that of element/status effect attributes shown below, and is the same debuff in bold every time that color/element fetter spawns. For posterity, I list out all of the elemented-aligned debuffs on one line. For the purposes of Sortie fetters, the debuff that is applied by the fetter is in bold. For example, a red/fire fetter always gives you the Burn/MAB Down/INT Down effect. (Do subsequent red fetters give you a different Fire-based debuff? I have no idea.)

Fire: Addle, Amnesia, Virus, Burn, MAB down, INT Down, Nocturne
Ice: Paralyze, Bind, Frost, Eva Down, AGI Down
Wind: Silence, Gravity, Choke, Def Down, VIT Down
Earth: Slow, Petrify, Rasp, Acc Down, DEX Down
Thunder:Stun, Shock, MND Down
Water: Poison, Drown, STR Down, Atk Down, M. Def Down
Light: Dia, Repose, Finale, Charm, Lullaby, Sheep Song, MACC Down
Dark: Blind, Bio, Sleep, Dispel, Geist Wall, Drain, Curse, Doom, Zombie, M. Eva Down, HP Down, MP Down, CHR Down, Absorbs
(Note: This element list is also in the order of the elemental wheel, Fire->Ice->Wind->Earth->Thunder->Water. Meanwhile, Light/Dark are opposites/opposing elements)

Subsequent fetters apply a cumulative Stat Down effect. A few folks in this thread say say this effect is approximately -161 Stat Down is applied per fetter.

Standing in place, while fighting against fetters and then dying, is not a "low DPS" or even "healing" problem.

It appears to be a low DPS problem when the proper mitigating responses aren't taken by the party: i.e. proc element + move away from the fetter. (Be sure to move as a group, as spread-out fetters is very problematic for applying debuffs over a larger area and affects more members of the party).

Another optimization for folks: If you're trying to calibrate your party's DPS and determine which bosses to do next, consider switching from DHABC(GEF) to (GFE) instead. You can save time by skipping Botulus from F>E, which is much riskier to skip Botolus if you do E>F, instead.

Don't assume your party lacks DPS because a boss wasn't proc'ed properly. Be cognizant of the fetter's debuffs and your positional arrangement on the field.