Quote Originally Posted by AvenoMatt View Post
MNK as Brotherhood on a 90s cooldown that may only boost physical dmg by 5% but it's a straight up dmg boost compared to Battle Litany that is only 10% crit chance boost which also has double the recast time of 180s.

MNK also has Mantra which though isn't a dps buff it buffs healing by 20% and is on a 90s cooldown. Drug's other buff may be a dmg buff of 5% but it only effects one other party member and is on a 120s cooldown. MNK buffs are more frequent and reliable while one of DRG's only helps with crit rng and the other only boosts on party member both of which have long cooldowns.
Just looking at how the damage is split out, RNG as a DPS buff isn't a problem because statistically it's going to average out over the course of a fight, as is the nature of random chance. Case in point, if you look at how FFlogs breaks out the DPS contributions for buffs, Brotherhood ends up being about 100 DPS less than Battle Litany, and you're really undervaluing Dragon Eye also, which adds up to ~200 DPS over the course of the fight.

The other thing you're forgetting is Monk's output is variable and highly party comp dependent. A Monk with a Dragoon will perform better than a Monk without one because of how strongly Monk benefits from the crit buff. Brotherhood's overall effectiveness also varies with the party composition, so a Monk in a caster heavy party will be performing worse than a Monk in a standard composition.