I believe it's the opposite. The dragons are still powerful enough to fight back and win, especially if they band together.
And it was the drakes that killed Malygos, since in the last third of the fight we weren't doing anything, it was the dragons doing all the fight.Canonically 25-ish mortals killed an Aspect with minimal assistance, Alex sent drakes to aid in the killing of Malygos she didn't personally empower us (unless Im misremembering).
Didn't they have a powerful artifact during that time that allowed them to control/tame dragons? Don't remember its name, but it was the chain that once held the Dragon Soul, if memory serves.Plus the Dragonmaw unaided killed plenty black dragonkin in Twilight Highlands, maybe not full dragons. (Edit: Correction they also killed full dragons).