Not entirely true. Witches can screw up dragon attacks. How? Well usually most of us keep cc in centre during wars. When drags start coming towards centre and trigger the CC, witch comes out and spawns few skeletons. Now many people use King for funelling dragons. If king or any ground troop is deployed and witch is still alive, her skeletons run to attack the ground troops. At the same time drags if nearby run behind skeletons screwing up the attack.
To counter this, just deploy the king when cc is destroyed and never use ground troops in Dragon attack or lure the cc troops to kill them. Drags are powerful enough to kill cc troops with ease.