Ast dps is still lower than the two other, yes, but not that much.
What's make the difference in the final resultat is that :

- It looks harder to dps as an Ast cause you're relying more on the Malefic III spam.
- You have less oGCD healing, so you have to take one GCD to heal sometime
- The clipping is strong in ast toolkit. Drawing every 30s + spread or royal road or shuffle/lord of crown...

At least, if the clipping could be avoided a little more, well ast could do a little better.

So all of this is ast dps in real situation.
But its true dps isn't that far from the other (still the weakest however).