Taking a quick glance at the job itself, it's very much single-target, kill-it-as-fast-as-you-can styled gameplay. Ninja will probably be good in short fights or speedruns while Monk will thrive in the long haul.

And, as always, if a person is bad at the job, they won't do well. Both jobs, it seems, will require a bit of thought to work out, and there is currently no faceroll, easy DPS class in the game so far (yes, even DRG has thought put into its rotations). I don't think Monks will be sitting on the sidelines.