I did a rough simulation based on the numbers we know for damage and potency and auto attack and found that in an ideal world with no misses and no down time a monk will always out DPS a ninja because a monks Auto Attacks will always be greater than any other DPS class due to the 52% bonus in damage a monk can obtain. However the more a monk loses its grease lightning stacks the more even it makes NIN til a point where NIN will surpass it.

Bottom line: Monk will always win in non phase changing / low movement fights, but things even out the more a monk has to refresh GL3 and dodge attacks.