I main a DRG, and all i can say is that a DRG can match and beat a MNK 9 times out of 10 at i90.
That being said there are very few DRG's that i see doing this, and very few MNK's that are able to be compared to.
It's just really really hard to play either class at such a high level, and most aren't willing to practice that hard for it.
On Twintania as DRG I'm always #1 DPS.
You just gotta know what ur doing and be willing to work for it