There is a massive difference between Wombo and Firebolt. If you are hit by a Wombo, your health will regen in a few seconds, assuming you live. If you are hit by a Firebolt, your health is lowered for 14 seconds. Their DoTs act quite differently. You might as well say, "Doctrine of Passing is overpowered, therefore Abyss Defiant is too!". Yeah, they do the same thing, but they do it differently.