MNK's DK is the most useful raid utility of all 3 melee jobs for progression. NIN's TA/Goad are a close second, and DRG at 3rd (possibly tied with NIN if your BRD isn't a bad). Outside of progression, if DK isn't needed then NIN shoots to the top, DRG at 2nd, and MNK at 3rd. MNK simply doesn't provide as much raid DPS as NIN and DRG, who already do comparable damage on their own. I guess everyone's still stuck in the mindset that "MNK is the 'hard to play' job, so obviously it's always going to be the highest DPS!". It's not. However, the difference between all 3 jobs is so minimal that it literally doesn't matter outside of progression, in which case you'd probably bring a MNK + NIN/DRG because DK is more important than a bit of extra DPS when it comes to learning a fight.

inb4 "nah but mnk iz so good da greased lightning omgz"