Step 1: Nerf most of the damage masteries. Good. Step 2:

Nerf all the keystones too.

Nerf them all equally.

> "but CotC just got nerfed twice"

Thats irrelevant as long as its getting nerfed proportionately to the rest.

> "But Grasp and BoS are already bad"

For the sake of fairness, hit them all equally at first. They can go back and make adjustments later. Well lets be honest maybe just replace BoS