In term of buff, Ninja is 22% down from Monk(GL 3 + FoF + Twin Snake).
Because of that, Ninja's auto-atk will be 22% (assuming additive coefficience) less than Monk's and auto-atk is roughly 30% of mDPS.
Most Monk' skill are roughly 10% poetency lower than Ninja other than Shadow Fang which is definitely strong with 440 potency (i didn't get the 790 potency you present).
From my estimation, it seems Ninja personal ST dmg is 5-10% lower than monk. In term of AoE, Ninja doesnt seem to have a lot of attractive option.
I am pretty happy with thh fact that Ninja dmg is lowee than monk which it should. A lot of their potential damage is from TA's debuff so they shouldn't have higher dps than monk. I would say Ninja should have even lower ST dps than Dragon.

Just my 2 cents