Break the Trinity System Please

[Duelle]

Do you remember what it was for? Im thinking it was something to do with shields.

Shields, shield blocking and so on. The shield blocking skills GLA and PLD currently have are based on some of the stuff you got from Sentinel.

You forgot Bard, most do. If there is a BLM/SMN in your party a Bard can directly affect DPS by using Foe Requiem ballad for, I think, 10% boost to dmg taken by mobs from magic damage. It could also be used to increase a healer's DPS if you really wanted to, but that could get questionable and/or risky depending on how much healing they need to be doing.

This only applies if everyone in the raid were a magic user, which is not always the case. If the group is caster-heavy (as in, your DPS are all either BLM or SMN) then yes, a BRD with Foe's Requiem up will notably affect damage output.

The context of what I'm talking about is stuff that affects everyone. NIN pretty much has the only debuff in the game that increases everyone's damage. That's akin to Icy Talons (+Haste rating to everyone in the raid so long as the DK kept it up), 4.0 Blessing of Might (increases everyone's main stat by X%), or 3.0 Sanctified Retribution (directly increased damage taken from all sources by the mob).