Yes, they are exaggerating. Dragoons are ahead, but not by a considerable amount. If the same player was equally skilled across all three Jobs, it'll definitely go Dragoon > Monk > Ninja on a single target, but with a 10-20 DPS difference between them.

Player skill is a huge factor in this however, which many people still forget. EG, the Monk in my Static blows every Dragoon out of the water and even out DPS's myself. He does have a gear advantage over myself obviously, but one small mess up and he's easily 100 DPS ahead. That's how close the differences are.