Are you level 50?

MNK requires more effort/timing to optimize dps than either class you're comparing it to, and they seem to scale better as your gear gets top end. A tweak or two maybe, but no- in general they are not lower dps.

Even if your rotations are bad- keeping GL up is the key. If the fight precludes you from keeping GL up constantly, then yes, you'll fall below other dps class damage.