There certainly are units that can fill some part of Karma's niche. But currently on nutaku the only one is Olivie and that's only against physical.

As lolix said, even a full cost Karma is great. Her value lies in her skill and it will always be useful as there is no other unit in game that can turn completely immortal for 13 seconds like she does. There are units that can do similar things, but not turn completely immortal.